Composition for non-crosslinked foam

Abstract: An expandable composition for non-crosslinked foam comprising (A) 80 to 99% by weight of a 1-butene polymer, (B) 20 to 1% by weight of an ethylene polymer, and (C) a blowing agent, the percentages being based on the total weight of the 1-butene polymer and the ethylene polymer.

Description: This invention relates to a composition suitable for producing a non-crosslinked foam composed of a major proportion of a 1-butene polymer, a minor proportion of an ethylene polymer and a blowing agent. Plastics foam products find wide applications in the fields of automobiles, household appliances, packing members, clothes, food, medical products, as thermally insulating materials and cushioning materials by making use of their light weight, thermal insulating properties and cushioning properties. Properties required of foam products are generally light weight, thermal insulating properties and cushioning properties. However, in accordance with various needs in the world, new foams having new characteristics, for example, more flexible foams or foams having excellent heat resistance have been increasingly demanded. There are many plastics materials used in foam products. Of these, typical thermoplastic resins are high-pressure low-density polyethylene and polystyrene. These resins have been used as foam products naturally by focussing attention on their mechanical properties but due largely to ease of expansion molding. Though the high-pressure low-density polyethylene and polystyrene have excellent expandability, they have poor heat resistance, and their maximum use temperature is about 80°C to about 90°C; they cannot be used at a high temperature above 100°C. Meanwhile, in the aspect of heat resistance, polypropylene is excellent, but polypropylene alone can hardly give a uniform foam. Japanese Patent Publication No. 40,167/1981 discloses a foam prepared from a mixture of 90 to 30% by weight of polypropylene and 10 to 70% by weight of polybutene-1. The patent publication states that this foam has excellent heat resistance, high-temperature creep characteristics, mechanical strength and thermal insulating properties and is suitable for use as a thermally insulating material for high-temperature structures. It also states that when the mixing proportions of polypropylene and polybutene-1 fall outside the above-specified ranges, a good foam cannot be obtained. Japanese Laid-Open Patent Application No. 129,025/1983 discloses a polyolefin foam prepared from a mixture of (a) 60 to 98% by weight of a propylene/ethylene block copolymer having a melt index of 0.5 to 2.0 and an ethylene content of 5 to 15%, (b) 1 to 20% by weight of polybutene or a butene copolymer having a melt index of 2 to 10, and (c) 1 to 20% by weight of low-density polyethylene having a melt index of 2 to 10. EP-A-147 690 discloses foamed particles of a non-crosslinked resin mixture of 10 to 95% by weight of an alpha-olefin/propylene random copolymer and 90 to 5% by weight of an ethylene/propylene random copolymer. However, the foams described in the above documents are, though excellent in heat resistance, poor in flexibility because they are too hard owing to mechanical properties of polypropylene, and cannot be used as thermally insulating materials of curved piping portions and packing materials of bottle closures requiring flexibility. When the foams are used as thermally insulating materials for clothes and cushioning materials of medical products, they are required to be better in flexibility and elastic recovery than the conventional foams. Like polyethylene and polypropylene, poly-1-butene is a polyolefin resin having flexibility and heat resistance and excellent in high-temperature creep characteristics in particular. Moreover, a copolymer of 1-butene and another alpha-olefin is used in the field requiring flexibility and creep resistance because when the content of alpha-olefin increases, the melting point lowers and heat resistance also decreases but flexibility improves. The 1-butene polymer thus possesses such excellent characteristics but is similar in viscoelasticity to polypropylene. Therefore, like polypropylene, the 1-butene polymer alone can hardly afford a uniform foam. US-A-4,359,544 discloses a composition comprising a 1-butene polymer, as small as 0.02 to 5.0 % by weight of stearamide and as small as 0.02 to 5.0% by weight of high-density polyethylene, said composition having high crystallisability and providing a film having improved tensile strength, modulus of elasticity and creep resistance. Said U.S. Patent however makes no mention of foams. An object of this invention is to provide a novel expandable composition that gives a non-crosslinked foam suitable for use as a thermally insulating material, a cushioning material and a capliner material having excellent flexibility, heat resistance, creep resistance, cushioning properties and hygienic properties. According to this invention, there is provided an expandable composition for use in producing a non-crosslinked foam comprising (A) 80 to 99 % by weight of a 1-butene homopolymer or a 1-butene copolymer composed of at least 70 mole % of polymerized units of 1-butene and not more than 30 mole % of polymerized units of an olefin having 2 to 20 carbon atoms other than 1-butene, said 1-butene polymer having a melt flow rate of 0.01 to 50 g/10 min, (B) 20 to 1 % by weight of an ethylene homopolymer or an ethylene copolymer composed of at least 90 mole % of polymerised units of ethylene and not more than 10 mole % of polymerised units of an a-olefin having 3 to 20 carbon atoms, said ethylene polymer having a melt flow rate of 0.01 to 50 g/10 min, and (C) a blowing agent in an amount of 0.2 to 30 parts by weight per 100 parts by total weight of the 1-butene polymer (A) and the ethylene polymer (B), the percentages being based on the total weight of the 1-butene polymer (A) and the ethylene polymer (B). The invention also provides a non-crosslinked foam obtainable from the expandable composition. The 1-butene polymer (A) used in this invention is a homopolymer of 1-butene or a copolymer composed of at least 70 mole%, preferably at least 80 mole%, of polymerized units of 1-butene and not more than 30 mole%, preferably not more than 20 mole%, of polymerized units of an olefin having 2 to 20 carbon atoms other than 1-butene. Examples of another olefin having 2 to 20 carbon atoms include ethylene, propylene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-tetradecene and 1-octadecene. The 1-butene polymer (A) is a crystalline polymer preferably having a melt flow rate [MFR(E):ASTM D1238, E] of 0.01 to 50 g/10 min., preferably 0.05 to 20 g/10 min. When MFR(E) is less than 0.01 g/10 min., melt extrusion is hard to perform at the time of expansion molding. When it exceeds 50 g/10 min., melt viscosity is low and expandability is poor. The ethylene polymer (B) is a homopolymer of ethylene or a copolymer composed of at least 90 mole%, preferably at least 95 mole% of polymerized units of ethylene and not more than 10 mole%, preferably not more than 5 mole% of polymerized units of an alpha-olefin having 3 to 20 carbon atoms. Examples of the alpha-olefin having 3 to 20 carbon atoms include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-tetradecene and 1-octadecene. The ethylene polymer (B) is preferably a polymer having a melt flow rate [MFR (E): ASTM D1238, E] of 0.01 to 50 g/10 min., preferably 0.03 to 30 g/10 min. Where MFR (E) is less than 0.01 g/10 min., melt extrusion is hard to perform at the time of expansion molding. Where it exceeds 50 g/10 min., melt viscosity is low and expandability is poor. The ethylene polymer (B) is preferably a crystalline polymer and has a density of at least 0.920 g/cm³, preferably at least 0.940 g/cm³, more preferably at least 0.950 g/cm³. Examples of the blowing agent (C) used in this invention include evaporatable blowing agents, for example, fluorinated aliphatic hydrocarbons such as trichloromonofluoromethane and dichlorotetrafluoroethane, and aliphatic hydrocarbons such as propane, methyl chloride, isobutane, pentane and hexane; and decomposable blowing agents such as sodium bicarbonate, ammonium carbonate, azodicarbonamide, barium azodicarboxylate, N,N'-dinitrosopentamethylenetetramine, 4,4-oxybis(benzenesulfonyl hydrazide), diphenylsulfone-3,3-disulfonyl hydrazide, p-toluene-sulfonyl semicarbazide, trihydrazinotriazine and biurea. These blowing agents can be used singly or in combination. Among these blowing agents, it is preferable to use singly or conjointly fluorinated aliphatic hydrocarbons such as dichlorotetrafluoroethane chemically stable and having a great evaporation latent heat, and azodicarbonamide and sodium bicarbonate in which an amount of gas generated is large and a temperature of terminating formation of a gas is much lower than a heat deterioration starting temperature of a 1-butene polymer (A)/ethylene polymer (B) mixture. The expandable composition of this preferably comprises 90 to 98% by weight of the 1-butene polymer (A) and 10 to 2% by weight of the ethylene polymer (B). The composition may contain, in addition to the 1-butene polymer (A), the ethylene polymer (B) and the blowing agent (C), a low-crystallinity or amorphous olefin random copolymer in such amount as not to impair the objects of this invention, for example, not more than 20 parts by weight per 100 parts by weight of the mixture of the 1-butene polymer (A) and the ethylene copolymer (B). Examples thereof are a propylene/1-butene random copolymer, a propylene/ethylene random copolymer, an ethylene/1-butene random copolymer, an elastomer such as an ethylene/propylene terpolymer, and other low-crystallinity polyolefins such as polypropylene, poly-4-methyl-pentene and an ethylene/vinyl acetate copolymer. When the ethylene polymer (B) is less than 1% by weight, no good foam is obtainable. When it exceeds 20% by weight, expandability becomes poor owing to bad compatibility, making it impossible to provide a good foam. The amount of the blowing agent (C) is properly adjusted depending on an intended foam. It is 0.2 to 30 parts by weight, preferably 0.5 to 20 parts by weight based on the total weight, 100 parts by weight, of the 1-butene polymer (A) and the ethylene polymer (B). When the amount of the blowing agent (C) is less than 0.2 part by weight, it is unlikely that a foam having a good expansion ratio could be obtained. As a method for producing a non-crosslinked foam using the composition of this invention, a so-called extrusion foaming method can be taken wherein the composition comprising the 1-butene polymer (A), the ethylene polymer (B) and the blowing agent (C) is extruded from a die in molten or softened state to expand a gas generated from the blowing agent contained in the composition at high to normal pressures. The composition used in this invention can contain, besides the blowing agent, additives ordinarily used in polyolefins, such as heat-resistant stabilizers, slip agents and antistatic agents in such amounts as not to impair the objects of this invention. The non-crosslinked foam obtained from the composition of this invention may be in various forms such as sheets, pipes, rods and tubes by properly changing a die of an extrusion molding machine. The composition of this invention allows easy expansion molding without cross-linking compared to 1-butene polymer which is difficult to use in expansion molding without crosslinking. The resulting foam of this invention is made of uniform, fine closed cells. Moreover, as the composition is composed mainly of the 1-butene polymer, it is better than the ordinary high-pressure low-density polyethylene foam and polystyrene foam in heat resistance, flexibility, creep resistance, cushioning properties and hygienic properties. These foams can properly be used in thermally insulating materials of high-temperature structures and packing materials requiring high-temperature sterilization treatment, such as bottle closures. The following Examples illustrate this invention in more detail. Example 1: One hundred parts by weight of a resin mixture (PB-I + HDPE) composed of 95% by weight of a 1-butene homopolymer [PB-1: MFR (E)=2 g/10 min., melting point: 125°C] and 5% by weight of high-density polyethylene [HDPE; MFR (E)=0.1 g/10 min., density 0.960 g/cm³, melting point 132°C] was mixed by a tumbler with 0.5 part by weight of azodicarbonamide (ADCA; Vinfor AC#6, a tradename for a product of Eiwa Chemical Industry Co., Ltd.) as a blowing agent. Subsequently, the mixture was melt-kneaded in a single-screw extruder (screw diameter 40 mm, set temperature 190°C) and extruded from a pipe-forming die (set temperature 120°C) to form a pipe-like foam. The resulting foam was of a smooth surface and had an apparent specific volume (volume/weight found from an external size) of 2.1 and a true specific volume (measured by an air compression picnometer of Beckman) of 2.0. It was a good foam made of uniform, fine closed cells. Examples 2 and 3: Example 1 was repeated except that the proportion of HDPE was changed as shown in Table 1. As a result, a foam made of uniform, fine closed cells and having a smooth surface was obtained as shown in Table 1. Examples 4 and 5: One hundred parts by weight of a resin mixture (PB-II + HDPE) composed of a 1-butene/ethylene random copolymer [PB-II: MFR (E)=0.2 g/10 min., ethylene content 12 mole%, melting point 103°C] and HDPE used in Example 1 in amounts shown in Table 1 was mixed by a tumbler with 5 parts by weight of ADCA as a blowing agent. The mixture was then melt-kneaded in a single-screw extruder (screw diameter 40 mm; set temperature 190°C), and extruded from a pipe-forming die (set temperature 95°C) to afford a pipe-like foam. The resulting foam was made of uniform, fine closed cells and had a smooth surface as shown in Table 1. Comparative Example 1: Example 1 was followed but using PB-I alone. The cellular film of the obtained foam was broken, the surface was heavily uneven and the specific volume was low. Comparative Example 2: Example 1 was followed but using PB-I and HDPE in amounts shown in Table 1. There was a big difference between the apparent and true specific volumes of the resulting foam and said foam was seen to be open-cellular, and small raisings and depressions were observed on the surface. Comparative Example 3: Example 4 was followed but using PB-II alone. The cellular film of the obtained foam was broken, the surface was heavily uneven and the expansion ratio was low. Thus, the foam was not good. Comparative Example 4: Example 4 was followed but using PB-II and HDPE as shown in Table 1. The surface of the obtained foam was not so heavily uneven as in Comparative Example 3 but had small raisings and depressions. Moreover, there was a big difference in apparent and true specific volumes of the foam, and the foam appeared to be open-cellular.

Claims: An expandable composition for use in producing a non-crosslinked foam comprising (A) 80 to 99% by weight of a 1-butene homopolymer or a 1-butene copolymer composed of at least 70 mole % of polymerized units of 1-butene and not more than 30 mole % of polymerized units of an olefin having 2 to 20 carbon atoms other than 1-butene, said 1-butene polymer having a melt flow rate of 0.01 to 50 g/10 min, (B) 20 to 1% by weight of an ethylene homopolymer or an ethylene copolymer composed of at least 90 mole % of polymerised units of ethylene and not more than 10 mole % of polymerised units of an α-olefin having 3 to 20 carbon atoms, said ethylene polymer having a melt flow rate of 0.01 to 50 g/10 min, and (C) a blowing agent in an amount of 0.2 to 30 parts by weight per 100 parts by total weight of the 1-butene polymer (A) and the ethylene polymer (B), the percentages being based on the total weight of the 1-butene polymer (A) and the ethylene polymer (B). A composition according to claim 1 which comprises 90 to 98% by weight of the 1-butene polymer (A) and 10 to 2% by weight of the ethylene polymer (B). A non-crosslinked foam obtainable from a composition as claimed in claim 1 or 2.

Inventors: KAGAWA FUKASHI, NAKASHIMA KOJI, TANAKA HARUHIKO, KAGAWA, FUKASHI, NAKASHIMA, KOJI, TANAKA, HARUHIKO
Applicants: MITSUI PETROCHEMICAL IND, SHELL OIL CO, MITSUI PETROCHEMICAL INDUSTRIES, LTD., SHELL OIL COMPANY
Application year: 1988
Main classification: C08J9
IPC codes: C08J9, C08L23