JP6890619B2 - Process for foaming polyolefin compositions using fluororesin as a nucleating agent - Google Patents

Description

The present invention relates to a process of foaming a composition. In one aspect, the invention relates to the foaming of a polyolefin composition using a fluororesin as a nucleating agent, and in another aspect, the invention relates to a foamed composition made from the process. In yet another aspect, the present invention
Concerning the use of the foamed composition as an insulating layer in telecommunications cables, especially high frequency coaxial cables.

Typically, the insulating layer of a radio frequency communication cable is nucleated with high density polyethylene (HDP).
Produced by mixing with a mixture of E) and low density polyethylene (LDPE).
These foaming materials are then injected into the polymer melt inside the extruder, such as nitrogen, carbon dioxide, chlorinated fluorocarbons, chlorofluorocarbons, helium, neon, argon, krypton, xenon, and radon. Extruded in the presence of a physical foaming agent such as gas. Nucleating agents for foaming include azodicarbonamide (ADCA) and 4,4'-oxybisbenzenesulfonylhydrazide (OBSH), which are pyrolyzed in the extruder and into the polymer melt. It forms a large number of fine nuclei. However, the degraded ADCA and OBSH by-products have high polarity, which is well known to have a significant negative effect on electrical performance (
Dissipative factor).

Compared to ADCA and OBSH, fluororesin powders such as polytetrafluoroethylene (PTFE) are nucleating agents that show significantly less effect on electrical performance, ADCA and O
It does not have the decomposition problems associated with BSH. PTFE has been and is still used as a nucleating agent for foaming compositions for use as an insulator in communication cables, but especially in effervescent compositions. Improvements are still desired in the dispersion of the forming agent, i.e., with respect to the polymer matrix and in the formation of small, uniformly sized cells in the foamed product.

The dispersion efficiency of the nucleating agent in the polymer matrix is mainly determined by the particle size and particle size distribution of the nucleating agent. USP3,554,932A is a finely divided solid fluororesin such as PTFE, fluorinated ethylene-propylene (FEP), or a particle carrier coated with fluorocarbon as a nucleating agent for the injected gas. It works and teaches that thermoplastics have been foamed. It also teaches that the particle size should not exceed 20 microns in diameter and that it should be used in an amount of 0.01% to 2% by weight.

EP386663 is a fluorocarbon powder used as a nucleating agent, which is 0.1 to 5 microns (
It teaches that it should have an average particle size of μm).

USP6,121,335 teaches a nucleating agent for foaming, wherein the nucleating agent is 0.
It contains a fluororesin powder containing particles having a particle size of 1 to 0.5 μm at a ratio of at least 50% on a number basis and particles having a particle size of 5 μm or more at a ratio of 40% or less on a number basis.

USP7,262,226 teaches the use of tetrafluoroethylene homopolymers (PTFEs) as nucleating agents with a number average molecular weight of less than 1,000,000, preferably less than 500,000. The nucleating agent is obtained by irradiating the PTFE powder produced by the dispersion or suspension polymerization process with γ-rays or electron beams, and then crushing the irradiated powder. The dispersion polymerization process gives a latex having a particle size of 0.1 to 0.3 micron. After solidification, the particle size of the powder increases to about 100-500 microns. The powder is irradiated with gamma rays and then crushed to give a powder with a final particle size of less than 15 microns. The suspension polymerization process gives a powder with a particle size of 2-5 mm. These powders are irradiated with an electron beam and then crushed to give a powder with a final particle size of less than 15 microns.

All of these references are greater than 1 micron, typically 5 microns, prior to the use of agents for foaming polyolefin compositions containing or consisting essentially of polyolefin compositions, especially HDPE and LDPE. It does not teach or recognize the benefits of reducing the size of ultrafluororesin nucleating agent aggregates (which produced dispersion polymerization) to less than 1 micron. Further, in any of these references, a foam composition can be prepared by batch mixing (eg, kneading) a reduced size nucleating agent, such as less than 1 micron, with a polyolefin resin. Not teaching or recognizing the benefits. These submicron nucleating agents are more evenly dispersed within the foam composition (similar in all aspects, but as opposed to the foam composition prepared by extrusion mixing), thus the foam composition is excellent. Provided are a foamed product having excellent foaming performance and excellent foaming performance, for example, a foamed product having a desired fine cell structure.

In one embodiment, the invention is a process for foaming a polyolefin composition, the process of which is a nucleating agent comprising 80% or 85% or more of non-aggregated fluororesin particles and / or aggregates of fluororesin particles. In the step of using, both the non-aggregated particles and the aggregates are less than a submicron size (ie, less than 1 micron (μm), typically 0.5 μm).
Includes steps that are m or less, more typically 0.3 μm or less in size). In one embodiment, the fluororesin nucleating agent is prepared by dispersion polymerization. In one embodiment, the effervescent polyolefin composition is formed by batch mixing the fluororesin nucleating agent and the polyolefin.

In one embodiment, the present invention is a process for foaming a polyolefin composition using a fluororesin nucleating agent containing 80% or 85% or more of aggregates having a size of 5 microns or more. The agglomerates contain submicron particles, and the process (A) reduces the size of the agglomerates to include 80% or 85% or more of particles or agglomerates less than 1 micron in size. A step of producing a forming agent, (B) a step of mixing the nucleating agent of (A) with a polyolefin to produce an effervescent composition, and (C) a step of effervescent the effervescent composition. including. In one embodiment, the nucleating agent and polyolefin of (B) are batch mixed.

In one embodiment, the present invention is a process for foaming a polyolefin composition, wherein the process is (A) a masterbatch of polyolefin and fluororesin (1).
) The fluororesin constitutes 1 to 50% by weight of the masterbatch, and (2) most, typically 80% or more than 85% of the fluororesin, is an agglomerate of submicron fluororesin particles. A step of preparing a masterbatch containing, and the size of the aggregate is 5 μm or more, and (B) the size of the fluororesin aggregate, 8 of the fluororesin in the masterbatch.
With the step of 0% or 85% or more containing or reducing fluororesin aggregates or fluororesin particles having a size of less than 1 μm, less than 0.5 μm, or less than 0.3 μm. (C) The step of mixing the masterbatch of (B) with a polyolefin to form a mixture of the fluororesin substantially uniformly dispersed in the polyolefin, and (D) the mixture of (C). Including the step of foaming. In one embodiment
Fluororesin is prepared by dispersion polymerization. In one embodiment, the mixture of (C) is prepared by batch mixing.

In one embodiment, the invention (A) reduces the size of the aggregate to 80% or 85.
A step of producing a fluororesin nucleating agent containing particles or aggregates having a size of% or more and less than 1 micron, and (B) mixing the nucleating agent of (A) with a polyolefin to produce an effervescent composition. A polyolefin foam produced by a process comprising: (C) foaming the effervescent composition. In one embodiment, the nucleating agent and polyolefin of (B) are batch mixed.

In one embodiment, the present invention is a polyolefin foam produced by a process of foaming a polyolefin composition, wherein the process is (A) a masterbatch of polyolefin and fluororesin, and (1) the fluororesin. Consists of 1 to 50% by weight of the masterbatch, (2) the majority of the fluororesin, typically 80% or 85% or more, contains agglomerates of submicron fluororesin particles, said coagulation. The steps of preparing a masterbatch in which the aggregate is 5 μm or larger, and (B) the size of the fluororesin aggregate in the masterbatch, 80% or 85% or more of the fluororesin in the masterbatch is less than 1 μm. Or 0.5
A step of containing or reducing the fluororesin aggregates or fluororesin particles having a size of less than μm or less than 0.3 μm to be essentially, and (C) mixing the masterbatch of (B) with polyolefin. The step includes forming a mixture of the fluororesin substantially uniformly dispersed in the polyolefin, and (D) foaming the mixture of (C). In one embodiment, the fluororesin is prepared by dispersion polymerization. In one embodiment, the mixture of (C) is prepared by batch mixing.

In one embodiment, the present invention is a cable comprising an insulating layer, comprising a foam produced by any of the processes of foaming the polyolefin composition described above.

In one embodiment, the present invention is a masterbatch comprising or essentially comprising a polyolefin and a fluororesin, wherein (1) the fluororesin is 1-5 of the masterbatch.
Consists of 0 weight percent and (2) most of the fluororesin, typically 80% or 85
% Or more include agglomerates and / or non-aggregated fluororesin particles of fluororesin particles, and both the agglomerates and the non-aggregated particles are submicron size. In one embodiment, the fluororesin is prepared by dispersion polymerization.

In one embodiment, the present invention is an effervescent composition, with reference to the weight of the composition.
(A) 45-95% by weight of HDPE and
(B) With 4 to 54% by weight of LDPE,
(C) 0.01 to 1% by weight of PTFE containing 80% or 85% or more aggregates of PTFE particles and non-aggregated PTFE particles, both of which are submicron size. , PTFE, and an effervescent composition comprising, or essentially becoming,
The PTFE is prepared by dispersion polymerization and the composition is prepared by batch mixing the HDPE, LDPE, and PTFE.

9 is a scanning electron microscope (SEM) image of a composition containing PTFE submicron aggregates and submicron non-aggregate particles prepared in Example 1 and dispersed in a polyethylene matrix. It is an SEM image of a composition containing agglomerated PTFE particles prepared in Comparative Example 1 and dispersed in a polyethylene matrix, and most of the agglomerates are over 1 micron in size. 6 is an SEM image of a foam prepared from the composition of Example 1. 6 is an SEM image of a foam prepared from the composition of Comparative Example 1. In Example 2, SEM of a composition containing PTFE submicron aggregates and submicron non-aggregate particles prepared by mixing in a ZSK-30 twin-screw extruder after batch mixing and dispersed in a polyethylene matrix. It is an image. In Example 2, it is an SEM image of a composition containing PTFE aggregates prepared by mixing in BUSS ™ Co-Kneader and dispersed in a polyethylene matrix, some of which are 5 microns. It is oversized. FIG. 2 is an SEM image of a composition comprising PTFE submicron aggregates and submicron non-aggregate particles prepared by mixing in a ZSK-30 twin-screw extruder and dispersed in a polyethylene matrix in Example 2.

Definitions All parts and percentages are weight-based and all test methods are filing dates of the present disclosure, unless otherwise indicated, implied by context, or customary in the art. It is the one at the time. Density is determined by ASTM D-792 and ASTM
Measured by MI with D-1238 (190 ° C./2.16 kg).

For the purposes of US patent practice, the content of any reference patent, patent application, or publication
In particular, with respect to the disclosure of definitions and general knowledge in the art (to the extent consistent with any definition expressly provided in this disclosure), the entire reference is incorporated by reference (or an equivalent US version thereof by reference). Will be used as such).

The numerical range in the present disclosure is an approximate value unless otherwise specified. The numerical range includes all values from the lower and upper limits, including the lower and upper limits, in increments of 1 unit, provided that there is at least 2 units between any lower and upper limits. The condition is that there is a separation. For example, compositional, physical, or other properties such as tensile strength, break point elongation, etc.
When 0 to 1,000, all individual values such as 100, 101, 102, etc., and 100 to
Subranges such as 144, 155-170, 197-200, etc. are intended to be explicitly listed. For ranges containing values less than 1 or fractions greater than 1 (eg, 1.1, 1.5, etc.), 1 unit is 0.0001, 0.001, 0.01 as needed. , Or 0.1. For ranges containing single digit numbers less than 10 (eg, 1-5), one unit is typically considered to be 0.1. These are merely examples of what is expressly intended and all possible combinations of numbers between the lowest and highest listed values are considered to be expressly set forth in this disclosure. As used herein, numerical ranges are provided specifically with respect to particle size and the amount of individual components in the mixture.

"Comprising,""inclusion,""having," and similar terms, with or without the presence of any additional components, steps, or procedures, whether they are explicitly disclosed or not. It is not intended to be excluded. To avoid any doubt, all processes claimed through the use of the term "comprising" are one or more additional steps, equipment parts or or unless otherwise indicated. It may include components and / or materials.
In contrast, the term "becomes essential" excludes any other component, step, or procedure from the scope of the subsequent description, except for those that are not essential to operationality. The term "consisting of" means any component, step, which is not explicitly described or listed.
Or eliminate the procedure. The term "or" refers to the members listed individually and in any combination, unless otherwise indicated.

"Composition" and similar terms mean a mixture of two or more materials.

"Polyolefin composition" and similar terms mean a composition comprising at least one polyolefin in the context of the present invention.

"Interpolymer" means a polymer prepared by the polymerization of at least two different monomers. The generic term includes copolymers commonly used to refer to polymers prepared from two different monomers, and polymers prepared from more than two different monomers, such as terpolymers, tetrapolymers and the like.

"Nucleating agent", "nucleating agent", and similar terms mean, in the context of the present invention, a substance, typically small particles, that provides a nucleation site for bubble formation within a polymer melt. To do.

The term "aggregate" and similar terms refer to the collection of two or more particle groups that together make up the whole. Aggregates can be of various sizes. The agglomerates are always larger than the particles from which they are made, but some particles that are not associated with a particular agglomerate can be larger than the agglomerates. In practice of the present invention, the initiating aggregates, i.e., as received from the manufacturer or supplier, are typically over 5 microns in size and are typically and preferably mixed with the polyolefin composition. And / or before foaming the polyolefin composition, the size is reduced to less than 1 micron, more preferably less than 0.5 micron, and even more preferably less than 0.3 micron.

"Particle" and similar terms mean unit mass. The particles can be of various sizes. Fluororesin particles, such as PTFE particles, are the unit mass of fluororesin. Two or more fluororesin particles that are grouped together, that is, in contact with each other, form a fluororesin aggregate. The fluororesin particles of the present invention typically and preferably have a size of less than 1 micron, more preferably less than 0.5 micron, and even more preferably 0.
It is less than 3 microns in size.

"Non-aggregated particles" and similar terms mean particles that are not associated with another particle of the same type. Non-aggregated particles include both particles dissociated from the aggregate and particles not associated with the aggregate.

"Masterbatch" and similar terms mean a concentrated mixture of additives in a carrier resin.
In the context of the present invention, the masterbatch comprises a concentrated mixture of fluororesin nucleating agents in a polyolefin resin. The masterbatch allows efficient addition of the nucleating agent to the polyolefin and dispersion in the polyolefin. The manufacture and use of masterbatch is well known to those skilled in the art of the manufacture and production of plastic and foam articles.

Polyolefins "Polyolefins" and similar terms are used, for example, ethylene, propylene, 1-butene,
It means a polymer derived from one or more simple olefin monomers such as 1-hexene and 1-octene. Olefin monomers can be substituted or unsubstituted, and if substituted, the substituents can be diverse. When the polyolefin contains unsaturateds, preferably at least one of the comonomeres is at least one unconjugated diene, eg, 1,7-octadiene, 1,9-decadien, 1,11-dodecadien, 1,13. -Tetradecazien,
7-Methyl-1,6-octadien, 9-methyl-1,8-decadien and the like. Many polyolefins are thermoplastic. Polyolefins include, but are not limited to, polyethylene, polypropylene, polybutene, polyisoprene, and various interpolymers thereof.

In one embodiment of the invention, the polyolefin is at least one of high density polyethylene (HDPE) and low density polyethylene (LDPE), preferably a combination thereof. HDPE resins that can be used in the practice of the present invention are well known, commercially available and available.
It can be prepared in a slurry reactor, gas phase reactor, or solution reactor using either Ziegler-Natta, chromium-based, constrained geometric, or metallocene catalysts. HDPE, as used herein, is at least 0.94 g / cc, or at least 0.94 g / cc.
Density of ~ 0.98 g / cc and melting index of 0.1 g / 10 min to 25 g / 10 min (MI,
It is an ethylene homopolymer or an interpolymer having _{I 2).}

HDPE may include ethylene and one or more C _3- C ₂₀ α-olefin comonomer. The comonomer (s) can be linear or branched. Non-limiting examples of suitable comonomer include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, and 1-octene. HDPE interpolymers are at least 50 weight percent ethylene-derived units, ie polymerized ethylene, or at least 70 weight percent, or at least 80 weight percent, or at least 85 weight percent, or at least 90 weight percent, or at least 95 weight percent.
Contains a weight percent polymerized form of ethylene.

In embodiments, HDPE has a density of 0.94 g / cc to 0.98 g / cc and 0.1 g.
A homopolymer or ethylene / α-olefin copolymer having a melt index of / 10 min to 10 g / 10 min. In the embodiment, HDPE is 0.960 g / cc to 0.980 g.
It has a density of / cc and a melting index of 0.1 g / 10 min-10 g / 10 min. In embodiments, HDPE has a density of 0.96 g / cc to 0.97 g / cc and 0.1 g / 10 min-10 min.
It has a melting index of g / min. In the embodiment, HDPE is 0.96 g / cc to 0.98 g.
It has a density of / cc and a melting index of 1.0 g / 10 min to 10.0 g / 10 min.

Non-limiting examples of suitable commercially available HDPE include, but are not limited to.
The Dow Chemical Company Midland and Michi, respectively.
DOWN High Density Polyeth available from gan, USA
Yrene resin and CONTINUM ™ and UNIVAL ™ high density polyethylene resin, ELITE ™ 5960G, HDPE KT 10000 UE,
HDPE KS 10100 UE and HDPE 35057E, Nova Chem
icals Corporation, Calgary, Alberta, Canada
SURPASS ™, available from Borealis, BS available from Borealis
2581, Hostalen AC available from Lyondell / Basell
P 5831D, RIGIDEX® HD5502S available from INEOS Offices & Polymers Europe, SABIC® B5823 and SABIC® B5421 available from SABIC, and HDPE 5802 and BM59 available from Total. Can be mentioned.

LDPE resins that can be used in the practice of the present invention are also well known and commercially available and can be any of a variety of processes including, but not limited to, solutions, gases, or slurry phases, and high pressure tubes or autoclaves. Made by thing. Polyethylene can also be homogeneous or heterogeneous with respect to the comonomer distribution. Homogeneous polyethylene usually has an essentially uniform comonomer distribution. On the other hand, heterogeneous polyethylene does not have a uniform comonomer distribution. In one embodiment, the LDPE is a linear low density polyethylene (LLDPE).
). In one embodiment, the LDPE is ultra-low density polyethylene (VLDPE).

Polyethylene has a wide molecular weight distribution characterized by a polydispersity (Mw / Mn) greater than 3.5, or a narrow molecular weight distribution characterized by a polydispersity (Mw / Mn) in the range of about 1.5 to about 3.5. It can have a molecular weight distribution. Mw is defined as the weight average molecular weight and Mn is defined as the number average molecular weight. They can be a single type of polyethylene, or a formulation or mixture of more than one type of polyethylene. Therefore, it can be characterized by either a single or multiple DSC melting points. Polyethylene can have a density in the range of 0.865 to 0.930 grams (g / cc) per cubic centimeter, preferably in the range of 0.9000 to 0.925 g / cc. They may also have _{a melt index (MI, I 2} ) in the range of 0.1 to 50 grams (g / 10 min) per 10 minutes.
Typical catalyst systems that can be used to prepare these polyethylenes are USP4,30.
Magnesium / titanium-based catalyst systems, vanadium-based catalyst systems, such as USP 4,508,842 (homogeneous polyethylene) and 5,332,793, which can be exemplified by the catalyst systems described in 2,565 (homogeneous polyethylene). , 5,342,907, and 5,410
Chromium-based catalyst systems, such as those described in 003 (homogeneous polyethylene), eg, USP.
Metallocene catalyst systems such as those described in 4,101,445, eg, USP 4,937.
, 299 and 5,317,036 (homogeneous polyethylene), etc., or other transition metal catalyst systems. Many of these catalyst systems are often referred to as Ziegler-Natta catalyst systems or Philips catalyst systems. Catalytic systems that use chromium or molybdenum oxide on a silica-alumina support can be included herein. The typical process for preparing polyethylene is also described in the aforementioned patent. Typical field polyethylene formulations and processes, and catalyst systems for providing them, are USP 5,371,145 and 5,405.
, 901. As various polyethylenes, high pressure process (HP-LDPE)
Low density homopolymers of ethylene produced by, and high density polyethylene (HDPE) having a density greater than 0.940 g / cc can be mentioned. The conventional high pressure process is Int
rotation to Polymer Chemistry, Stille, Wi
Ray and Sons, New York, 1962, pp. 149-151. The high pressure process is typically free radical initiation polymerization performed in a tubular reactor or agitated autoclave. In a stirring autoclave, the pressure is about 10,000
It ranges from ~ 30,000 psi (about 69 to about 207 MPa) and the temperature is from about 175 ° C.
It is in the range of about 250 ° C. and in a tubular reactor, the pressure is from about 25,000 to about 45.
It is in the range of 000 psi (about 170 to about 310 MPa) and the temperature is about 200 ° C to about 3
It is in the range of 50 ° C.

The LDPE resin on the market is not limited, but for example, DFDB.
Use in rugged bags or agricultural films such as DOWN Low Density Polyethylene resins available from The Dow Chemical Company such as -1258 NT and generally, for example, those available from Borealis, Basel, Sabic et al. Any fractional for
Examples include melt flow index (MFI) resins.

The HDPE / LDPE mixtures or formulations of the present invention are dry-blended in any suitable means known in the art, eg, in pelletized form, in desired proportions, followed by screw extruder or BANBURY ™ mixing. It may be prepared by melting and blending in an apparatus such as a machine. The dry-blended pellets are, for example, by extrusion or injection molding.
It may be melt-processed directly into the final solid state article. The formulation may also be made by direct polymerization. Direct polymerization uses, for example, one or more catalysts in a single reactor or in two or more reactors in series or in parallel, at least one of operating conditions, monomer mixture, and catalyst selection. One may be varied.

The amount of HDPE in the polyolefin composition is typically at least 45 percent (% by weight), more typically at least 55 percent, and even more typically at least 60, based on the weight of the composition. Weight%. The amount of HDPE in the polyolefin composition typically does not exceed 95% by weight, more typically 8 based on the weight of the composition.
It does not exceed 5% by weight, and even more typically 80% by weight.

The amount of LDPE in the polyolefin composition is typically at least 4% by weight (% by weight), more typically at least 14% by weight, and even more typically at least 19 based on the weight of the composition. Weight%. The amount of LDPE in the polyolefin composition typically does not exceed 54% by weight, and more typically 44, based on the weight of the composition.
It does not exceed% by weight, and even more typically 39% by weight.

The HDPE constituents of the formulation may include two or more grades of HDPE, the LD of the formulation.
The PE component may include two or more grades of LDPE. The HDPE / LDPE formulation typically has 0.1-4 g / 10 min, more typically 0.15-4 g / 10 min I ₂ .

Fluororesin The fluororesin constituting the nucleating agent of the present invention can be various polymers including homopolymers and copolymers of fluorine-containing monomers. Examples of fluororesins that can be used in the practice of the present invention are, but are not limited to, polytetrafluoroethylene (PTFE),
Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA),
Ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride (PVdF), polychlorotrifluoroethylene (PCT)
FE), chlorotrifluoroethylene-ethylene copolymer (ECTFE) and the like. PTFE, PFA, and ETFE are preferred, with PTFE being particularly preferred.

In one embodiment, the fluororesin is prepared by dispersion polymerization (as opposed to suspension polymerization). Dispersion polymerization typically produces fluoropolymer particles of submicron size, such as 0.1 to 0.3 micron, which are often aggregates of size 5 microns or larger. , Tends to aggregate. One embodiment in the practice of this process comprises reducing the size of such fluororesin aggregates to submicron-sized aggregates and / or individual submicron particles forming the aggregates, the size reduction of which. Is carried out before foaming the mixture of fluororesin nucleating agent and polyolefin. In one embodiment, the fluororesin nucleating agent and polyolefin are mixed, preferably batch-mixed, after the fluororesin aggregates have been subjected to size reduction.

The shape of the fluororesin particles, which are typically in bulk form of powder, is not particularly limited, but the particles are predominantly spherical in order to produce foams containing fine cells and excellent uniform foaming. It is preferable to have.

Nucleating agent Fluororesin particles, especially those with a size of less than 1 micron, are prone to agglomeration. In one embodiment of the invention, the nucleating agent is at least one fluororesin, preferably PTFE. Some commercially available fluororesin powders, especially those made by dispersion polymerization, contain high concentrations of aggregates of at least 5 microns (μm) in size, such as diameter. Typically
The size of the agglomerates ranges from 4 to 50 microns, more typically 5 to 20 microns, and even more typically 5 to 15 microns. Typically at least 5μ in these powders
The amount of m-sized nucleating particles is at least 80%, more typically at least 82%, and even more typically at least 85%. These powders are, for example, HDPE and /
Or it does not disperse well in many polyolefins such as LDPE.

Aggregated fluororesin particles, i.e. aggregates, can be used in the practice of the present invention (1).
Less than micron, preferably less than 0.5 micron, and more preferably less than 0.3 micron in size distribution), but the use of non-aggregated particles is preferred. Therefore, the fluororesin nucleating agent used in the present invention was typically of submicron size in the first place.
Or non-aggregated particles that can be mixed with either one that has been reduced in size from more than 1 micron to less than 1 micron. The practice of the present invention is to some extent (eg, 10%, or 9%, or 8%, or 7 of total particles and / or aggregates mixed with polyolefin.
%, Or 6%, or 5%, or 4%, or 3%, or 2%, or less than 1%)
The presence of particles and / or agglomerates larger than 1 micron in size can be tolerated, but the smaller the amount of such particles and / or agglomerates, the better the dispersion of the particles and agglomerates in the polyolefin. The cell size in the foamed product is more evenly distributed.

The agglomerated particles can be separated from each other by any conventional means, such as by grinding, mixing, or stirring (typically at relatively high speeds). In one embodiment, a fluororesin nucleating agent containing agglomerates of 1 micron or larger, typically 3, or 4, or 5 microns or larger.
Most, preferably 80%, 8 of such aggregates before the nucleating agent is mixed with the polyolefin.
Subject to any procedure, treatment, etc. that will reduce 2%, 85%, 90% or more to either non-aggregated particles smaller than 1 micron or aggregates smaller than 1 micron. ..

In one embodiment, fluororesin nucleating agents containing aggregates of 1 micron or larger, typically 3, or 4 or 5 microns or larger, are first mixed with polyolefin to form a masterbatch, which is then said. The masterbatch is the majority of such aggregates, preferably 80%, 82.
%, 85%, 90% or more are subjected to any procedure, treatment, etc. that will reduce to either non-aggregated particles smaller than 1 micron or aggregates smaller than 1 micron. ..
Typically, the masterbatch is 1 to 50, more typically 5 to 50, even more typically 10 to 20 weight percent (% by weight) of nucleating agent, and 50 to 99, more typically. Is 70 ~
95, and more typically 80-90% by weight of polyolefin. After the masterbatch has been subjected to nucleating agent size reduction procedures, treatments, etc., the masterbatch will be subjected to a sufficient period of time under the condition that the foamed polyolefin and the non-aggregated particles and aggregates are uniformly dispersed in the polyolefin. Mixed before the start of the foaming process.

In one embodiment, a fluororesin nucleating agent containing agglomerates of 1 micron or larger, typically 3, or 4 or 5 microns or larger, is initially mixed with the polyolefin in the desired amount for the practice of the foaming process. The polyolefin is then (1) the majority of such aggregates, preferably 80%, 82%, 85%, 90% or more, non-aggregated particles less than 1 micron in size, or Any procedure, treatment that will reduce to any of the agglomerates less than 1 micron in size and (2) disperse these non-aggregated particles and the reduced agglomerates substantially uniformly in the polyolefin. It is provided for sufficient time.

The nucleating agent, especially the PTFE of the particle size distribution described above, is H by any conventional means.
It can be added to a polyolefin composition that contains or becomes essential to DPE and LDPE. The nucleating agent can be added unprocessed, eg, in combination with one or more other additives such as antioxidants, cell stabilizers, etc., or as part of a masterbatch. The nucleating agent is mixed with the polyolefin composition to achieve an essentially homogeneous dispersion of the nucleating agent of the polyolefin composition, and for this purpose typically, for example, through the use of BUSS ™ kneader. Batch mixing is preferred for mixing in the extruder. When the nucleating agent is first mixed with the polyolefin composition in an extruder, it is typically added to the polyolefin composition before injecting the gas for foaming.

The amount of nucleating agent added to the polyolefin composition is typically 0.01 to 1% by weight, more typically 0.05 to 0.5% by weight, based on the weight of the polyolefin composition. Even more typically 0.1 to 0.3% by weight.

The particle size can be determined by any method known in the art. In one embodiment, the determination of the particle size and ratio (% by number) of the fluororesin powder can be determined as follows. A dispersion containing ethanol and a fluororesin powder obtained by dispersion treatment for about 2 minutes under ultrasonic treatment at about 35 to 40 kHz, and the fluororesin powder is 70 to 9
The dispersion is contained in an amount that produces 5% laser transmission (ratio of output light to incident light), relative refraction (determined by the diffraction ratio of the fluororesin powder (about 0.99)) to ethanol. Microtrack particle size analyzer based on or closest to the ratio to the diffraction ratio (eg 1.02) and under continuous flow cell measurement mode The particle size of each particle (D ₁ , D ₂ , D ₃ ...) and the number of particles with each particle size (N ₁ , N ₂ , N ₃ ...) are optically diffracted by the laser. Determine based on. In this case, the particle size (D) of the individual particles is automatically measured by a Microtrack particle size analyzer in which particles of various shapes are measured in terms of the diameter of the corresponding sphere. Therefore, the particle size D
_{The ratio of 1} (% based on the number) is the total number of particles (ΣN) of the number of _{these particles (N 1).}
Expressed as a percentage of. The ratio of particles with a particle size of 0.1 to 0.5 μm is expressed as a percentage of the number of particles with a particle size of 0.1 to 0.5 μm to the total number of existing particles (ΣN). Similarly, the proportion of particles with a particle size of 5 μm or larger is
It is expressed as a percentage of the total number of existing particles (ΣN) of the number of particles having a particle size of 5 μm or more. On the other hand, the average particle size of the nucleating agent of the present invention is the total number of existing particles (ΣN) and the product of the cube of the particle size of each particle and the total number of existing particles (ΣN) according to the following formula.
It can be calculated using ND ^3).

The calculation of particle size is further illustrated in USP 6,121,335.

Additives The polyolefin composition used in the present invention may optionally or optionally contain one or more additives. Typical additives include, but are not limited to, processing aids, lubricants, stabilizers (antioxidants), foaming aids, nucleating agents, surfactants, flow aids, viscosity control agents. , Colorants, copper damage inhibitors and the like. These additives can be added to the polymer (s) either before or during processing. The amount of any particular additive in the polyolefin composition is typically 0.01-1% by weight, more typically 0.01-0.5% by weight, and even more typically 0. It is 01 to 0.3% by weight, and the total amount of additives in the polyolefin composition, if present, is typically 0.01 to 0.01 to 0.3% by weight.
It is 5% by weight, more typically 0.01 to 2% by weight, and even more typically 0.01 to 1% by weight.

Foaming agent The foaming agent is one or more suitable for extrusion temperature, foaming conditions, foam forming method and the like. When the insulating foam layer in the final form is formed at the same time as extrusion formation, for example, _{an inert gas such as nitrogen, carbon gas (for example, CO, CO 2,} etc.), helium, argon, for example, methane, propane, butane, etc. Hydrocarbons such as pentane, for example, halogenated hydrocarbons such as dichlorodifluoromethane, dichloromonofluoromethane, monochlorologifluoromethane, trichloromonofluoromethane, monochloropentafluoroethane, and trichlorotrifluoroethane are used. The amount of foaming agent used can vary. Typically it is 0.001 to 0.1 parts by weight, more typically 0.005 to 0, per 100 parts by weight of the polyolefin composition to be foamed.
.. 05 parts by weight. The foaming agent may be premixed with the organic polymer to be foamed, or may be supplied into the extruder through a foaming agent supply port formed on the barrel of the extruder.

Foaming Process The polyolefin compositions of the present invention are foamed using known methods and known equipment.
Typically, the foam uses an extruder that operates a polyolefin composition containing a nucleating agent under foaming extrusion conditions, such as injection of a foaming agent, when the composition is in a high pressure zone. The composition is then extruded and then extruded into a low pressure area. The foaming process is described in C.I. P. Park in Polyolefin Foam, Chapter 9, H
andbook of Polymer Foams and Technology,
D. Klemner and K.M. C. Frisch ed., Hanser Publicer
Further described by s (1991).

In one embodiment, a typical extrusion foaming process is CA 2523 861 C, Lo.
w Loss Foam Composition and Cable Haveing
Atmospheric gases (eg, CO) as described in Low Loss Foam Layer.
₂ ) is used to produce a foamed cable insulator. Dissolution of the foamed gas in the polymer melt can be described, for example, in H. It is governed by Henry's law, as reported in Zhang (below) and other studies. Solubility is a function of saturation pressure and Henry's law constant, which is itself a function of temperature. / Zhang_Hongtao_2010111_MAS
c_thesis. pdf. Similarly, Foam by the editor Sau-Tarng Lee
Extrusion: See also Principles and Practice. The MuCell® microcell foam injection molding technique is an example of a commercially practiced foaming process, which is generally described in USP 6,284,810.

Given the importance of proper pressure control during foam extrusion, a suitable process is commercially referred to as the MuCell process, in which US 6,84,
Appropriate pressure is built through specific hardware designs for effective nucleation, as reported in 810B1. The method disclosed in this publication relies solely on high pressure descent (dP / dt) for self-nucleation of effervescent gas in the absence of "auxiliary nucleating agents" (Col. 4,
Lines 25-30).

Embodiment of the present invention In one embodiment, the nucleating agent is prepared by dispersion polymerization.

In one embodiment, the foam composition is prepared by batch mixing.

In one embodiment, the polyolefin composition comprises at least two polyolefins.

In one embodiment, the polyolefin composition consists essentially of two polyolefins.

In one embodiment, the polyolefins in the polyolefin composition are HDPE and LDPE.

In one embodiment, the polyolefin composition comprises at least one nucleating agent.

In one embodiment, the polyolefin composition comprises at least one of an antioxidant and a cell stabilizer.

In one embodiment, the polyolefin composition comprises HDPE, LDPE, and PTFE.

Specific Embodiments The following experiments are provided to illustrate various embodiments of the present invention. They are not intended to limit the invention as otherwise described and claimed. All numbers are approximate.

Example 1 and Comparative Example 1
The material LDPE-1 is 2.3 g / 10 min MI (ASTM D-1238, (190 ° C./).
2.16 kg)) and low density polyethylene (LDPE) with a density of 0.92 g / cc (ASTM D-792).

PTFE-1 is a white free-flowing PTFE having an average particle size of ZONYL ™ MP 1400, 10 μm and is available from DuPont.

PTFE-2 is ZONYL ™ MP 1600, a white free-flowing PTFE with an average particle size distribution of 7 μm, available from DuPont.

SONGNOX ™ 1024 FG is a 2', 3-bis [[3- [3,5-di-t].
ert-Butyl-4-hydroxyphenyl] -propionyl]] propionohydrazide,
An antioxidant available from Songwon International-Americas, Inc.

LDPE-2 is DFDB-1258 NT, 6 g / 10 min MI (ASTM D-1).
238, (190 ° C./2.16 kg)) and density of 0.922 g / cc (ASTM D)
-792) is a low density polyethylene (LDPE), The Dow Chem
It is available from the ical Company.

HDPE is DGDA-6944 NT, 8 g / 10 min MI (ASTM D-123)
8, (190 ° C./2.16 kg)) and density of 0.965 g / cc (ASTM D-7)
92) is a high density polyethylene (HDPE) with The Dow Chemic
It is available from al Company.

Dispersion efficiency preparation The preparation follows a two-step approach, first with an internal mixing bowl (B equipped with a cam blade).
RABENDER ™ model Prep Mixer / Measurement Head
Using a laboratory electric batch mixer), a higher concentration masterbatch (MB) is prepared by batch mixing operation and then diluted in a twin screw extruder. Each test is started using conventional mixed cycle addition, where the polymer is added first, then the PTFE powder and the antioxidant are added in an increasing amount. The processing temperature setting point is 120 ° C., and the mixer load speed is 35 revolutions per minute (rpm). After the polymer resin begins to flow, it is filled with PTFE powder and an antioxidant. The time required for melt mixing is about 4 minutes. Prepared concentrated PTFE (20)
%) Nucleating agent MB is diluted into 10% PTFE MB on an 18 mm (mm) twin screw extruder (TSE-18) for the second mixing step to form PTFE nuclei in a polyethylene matrix. Achieve the desired dispersion of the agent.

The polymer matrix is formed in the foam through the use of a blowing agent. Preferably, the blowing agent is carbon dioxide (CO ₂ ). In one example, the polymer matrix is a polymer matrix at a temperature above the ambient,
_{After being placed in a container together with CO 2} at a pressure exceeding the surroundings, it is foamed by quickly reducing the pressure in the container. In one example, the blowing agent is supercritical CO ₂ . The critical pressure of CO _{2 is 7.4 MPa.} In one example, the desired pressure in the container is 25-35 MPa. In one example, the desired temperature in the vessel is 111 ° C to 130 ° C with respect to the polymer matrix in which the high density polyethylene forms the main chain.

The compositions of Comparative Examples 1 and 1 are reported in Table 1 along with the dispersion efficiency and particle size of the PTFE nucleating agent, as well as the various cell properties of the foamed product.

Characteristic of Extruded Foam Rod Expansion Ratio

The expansion ratio is calculated based on the density of the sample before and after foaming. The density of foamed articles and solid plaques is measured according to ASTM D792.

Average cell size The foamed sample is destroyed using liquid nitrogen and then slices are cut using a razor blade. Slices, EMITECH ™ before scanning electron microscopy (SEM) analysis
Coat with platinum using a K575X coater. SEM image, FEI Nov
Obtained on a NanoSEM 630 SEM by an Everhart Thornley detector (ETD) and a through-lens detector (TLD) with an acceleration voltage of 5 kV, a working distance of approximately 6.5 mm, and a spot size of 5. The average cell size is obtained through analysis of SEM photographs.

The cell density of the foamed article can be calculated by the following equation:

N _f represents the number of cells per cubic centimeter volume in the foamed article, and N _c is.
Is the number of cells in the visible region of the SEM photograph, Ac is the area of the SEM photograph, _{M c} is the magnification.

D is the average cell size and can be calculated by the following equation:

V _t represents the expansion ratio of the foamed article.

Results Figures 1A and 1B are scanning electron microscope images showing that different initial particle morphologies undergoing the same mixing process result in different particle dispersions. The aggregate of Example 1 first consists of submicron particles produced via dispersion polymerization and is uniformly redistributed into small individual particles in the polymer matrix. The aggregates of Comparative Example 1 are of the same size as those of Example 1, but are not homogeneously divided into small, uniform particles. The two nucleating agents are shown in FIG.
As shown in A and 2B, it results in a completely different foam structure.

Example 2
Extruder vs. Batch Mixer High Load Continuous Mixer (Biaxial Screw Extruder, BUSS ™ Kneader, Twi
Compared to n-rotor Farrel, JSW or Kobe machines), the internal batch mixer is a low load, low speed, ie low shear mixer with a long mixing time (about several minutes). In contrast, continuous mixers operate at much higher speeds, i.e. higher shear rates and lower residence times (typically 5-20 seconds). The following experiments compare the effects of these two mixed regimens on the dispersion of the nucleating agent in the polymer matrix and the resulting foamed product. This finding may be due to a mixing regimen with lower shear, but still higher dispersion force over longer residence times in order to achieve a more homogeneous dispersion compared to higher loading, shorter mixing times.

A twin-screw extruder WERNER & PFLEIDERER® ZSK-30, an 11-barrel twin-screw extruder is used to prepare a 10 wt% PTFE dispersion in LDPE-2. The extruder operates at a relatively moderate rate of 100 rpm and the melt discharge temperature is 170 ° C.

BUSS ™ Co-Kneader Batch Mixing MKS-70 BUSS ™ (Trademark) (20L / D) Using Co-Kneader, L
Prepare a 10 wt% PTFE dispersion in DPE-2. The machine operates at 250 rpm and the melt discharge temperature is 191 ° C.

The best resulting variance is that shown in FIG. 3A and, as can be seen, described above in FIG.
Compared to the batch method shown in FIG. 3B, the Buss dispersion shown in FIG. 3B contains larger particles of 5 microns or more, and under the same magnification, the smaller particles are larger than those in FIG. 3A.

The best dispersion is that shown in FIG. 3C. At first glance, the dispersion appears to be fairly uniform without the presence of large particles, but a non-negligible number of elongated regions are visible. A more detailed examination at higher magnification (inserted image) reveals an elongated needle-like area that looks like fibrotic PTFE, which is compressed and fibrillated in a high-load twin-screw extruder. Is likely to be the result of. The elongated fibril-like region is not known to function as a nucleating agent and would therefore be undesirable for the purposes of the present invention.
The present invention includes the following embodiments.
[1] A process for foaming a polyolefin composition using a fluororesin nucleating agent containing 80% or more of aggregates having a size of 5 microns or more, wherein the aggregates contain submicron particles. The process comprises (A) reducing the size of the agglomerates to produce a fluororesin nucleating agent containing 80% or more and less than 1 micron in size particles or agglomerates, and (B) said. A process comprising (A) mixing the nucleating agent with polyolefin to produce an effervescent composition and (C) effervescent the effervescent composition.
[2] The process according to [1], wherein the effervescent composition of (B) is prepared by batch mixing the nucleating agent of (A) with the polyolefin.
[3] A process for foaming a polyolefin composition, which is (A) a masterbatch of polyolefin and fluororesin, and (1) the fluororesin constitutes 1 to 50% by weight of the masterbatch. , (2) A step of preparing a masterbatch in which most of the fluororesin contains aggregates of submicron fluororesin particles, and the aggregates have a size of 5 μm or more, and (B) the fluororesin aggregates. To reduce the size of the fluororesin in the masterbatch such that 80% or more of the fluororesin in the masterbatch contains or is essentially fluororesin aggregates or fluororesin particles having a size of less than 1 μm. 3) The step of mixing the masterbatch of (B) with polyolefin to form a mixture of the fluororesin substantially uniformly dispersed in the polyolefin, and (D) foaming the mixture of (C). Steps and processes, including.
[4] The process according to any one of [1] to [3], wherein the fluororesin is prepared by dispersion polymerization.
[5] The process according to [4], wherein the polyolefin of the polyolefin composition comprises high density polyethylene (HDPE) and low density polyethylene (LDPE).
[6] The HDPE comprises 45-95% by weight of the composition based on the weight of the composition, and the LDPE comprises 4-54% by weight of the composition based on the weight of the composition. The process according to [5] that constitutes.
[7] The process according to [6], wherein the fluororesin contains polytetrafluoroethylene (PTFE).
[8] The process according to [7], wherein the PTFE is present in the composition in an amount of 0.01 to 1% by weight based on the weight of the composition.
[9] The process according to [8], wherein the composition further comprises at least one of an antioxidant and a cell stabilizer.
[10] A foam produced by the process according to any one of [1] to [3].
[11] A cable including an insulating layer containing the foam according to [10].
[12] A masterbatch containing or consisting essentially of a polyolefin and a fluororesin, wherein (1) the fluororesin constitutes 1 to 50% by weight of the masterbatch and (2) the fluororesin. A masterbatch in which the majority of fluororesin particles contain agglomerates and / or non-aggregated fluororesin particles, both of which are submicron-sized.
[13] An effervescent composition based on the weight of the composition.
(A) 45-95% by weight of HDPE and
(B) With 4 to 54% by weight of LDPE,
(C) 0.01 to 1% by weight of PTFE containing 80% or 85% or more aggregates of PTFE particles and non-aggregated PTFE particles, both the aggregates and the non-aggregated particles in submicron size. Yes, including PTFE,
An effervescent composition in which the PTFE is prepared by dispersion polymerization and the composition is prepared by batch mixing the HDPE, LDPE, and PTFE.

Claims (5)

A foam composition based on the weight of the composition.
(A) 60-80% by weight HDPE and
(B) 19-39 wt% LDPE and
(C) Aggregates and non-aggregated PTFE particles having a PTFE of 0.1 to 0.3% by weight and having a PTFE content of 80% or more based on the weight of the polyolefin composition containing HDPE and LDPE. seen including, both the aggregate and the non-agglomerated particles is less than 0.3 [mu] m, comprising a PTFE, the foam composition. The foam composition according to claim 1, wherein the foam composition has a cell size range of 18.8 μm to 30.4 μm. A cable comprising an insulating layer containing the foam composition according to claim 1 or 2. A masterbatch consisting of (1) 80 to 90% by weight of polyolefin, (2) 10 to 20% by weight of fluororesin, and (3) an antioxidant which is an optional component, and 85% or more of the fluororesin is A masterbatch containing agglomerates and / or non-aggregated fluororesin particles of fluororesin particles, wherein both the agglomerates and the non-aggregated particles have a submicron size of less than 0.3 μm. The masterbatch according to claim 4, wherein the polyolefin is LDPE.

Images