KR100493549B1 - Modified polypropylene resin composition with excellent bubbling property and foam prepared by using the same - Google Patents

Abstract

The present invention relates to a modified polypropylene resin composition having excellent foamability and a foam produced using the same, more specifically, a weight average molecular weight of 300,000 g / mol or more and a melt index of 0.1 ~ 10 g / 10 minutes (230 ℃) 80 to 99 parts by weight of polypropylene and 100 parts by weight of a mixed resin composed of 1 to 20 parts by weight of high viscosity low density polyethylene having a weight average molecular weight of 500,000 g / mol or more and a melt index of 0.1 to 0.5 g / 10 minutes (230 ° C.). 0.5 to 10 parts by weight of ethylene-propylene block copolymer having an ethylene / propylene ratio of 50/50 to 90/10 (w / w), 0.05 to 10 parts by weight of polyfunctional monomer, and 0.005 to 5 parts by weight of organic peroxide It relates to a modified polypropylene resin composition and a foam prepared by extruding the resin composition, the modified polypropylene resin of the present invention is increased by more than two times compared to the conventional resin by the introduction of side branches In addition to the demonstrated excellent foaming properties in the process, because it does not contain a cross-linking structure, unlike the conventional high melt tension polypropylene resin it is retained the properties of the thermoplastic resin as it has the advantage of being recyclable.

Description

Modified polypropylene resin composition with excellent bubbling property and foam prepared by using the same}

The present invention relates to a modified polypropylene resin composition having excellent foamability and a foam produced using the same, and more particularly, to a modified polypropylene resin composition having improved melt tension and foamability by introduction of side branches using a polyfunctional monomer, and It relates to a foam produced by extruding the resin composition.

In general, polypropylene is a general-purpose plastic having a relatively high strength and excellent mechanical properties compared to other resins, and this property is due to the crystal structure of the polypropylene molecule and the molecular structure of the polymer chain. Moreover, homopolypropylene has excellent resistance to deformation at high temperature, has high tensile strength and surface rigidity, and copolypropylene with irregular or block copolymerization of ethylene or butylene increases impact strength depending on the application.

On the other hand, polypropylene has been shown to be limited in foam production due to inferior foamability compared to other plastic materials due to weak melt tension due to linear chain structure. If the melt tension is weak, as in the case of polypropylene, the cell walls separating the bubbles are not strong enough to overcome the tensile force and easily collapse and rupture. As a result, the foamed polypropylene product has a high content of collapsed cells and unsatisfactory control of the cell structure. In addition, even in the case of vacuum molding or blow molding, sagging due to weak melt tension during heating of sheets or preforms is severe, and satisfactory moldability cannot be obtained.

Therefore, in order to overcome these problems, various methods for increasing the melt tension of polypropylene have been attempted. In International Publication No. 94/26794, a method of continuously producing polypropylene having high melt tension, A method of mixing and producing high molecular weight polypropylene and low molecular weight polypropylene by controlling the amount of hydrogen in different reactors is proposed. However, the mixed polypropylene by this method has a drawback that the zero viscosity, which is an index of melt tension, and the shear reduction phenomenon exhibit similar behavior to those of the existing polypropylene resin. Meanwhile, Korean Patent Publication No. 96-34301 proposes a method for reinforcing the melt tension of polypropylene by mixing polypropylene and polyethylene. However, polypropylene and polyethylene are inherently incompatible and have a certain drawing speed. Higher than this has the disadvantage that the melt tension is lower than pure polypropylene.

As an alternative to this, recently, a method of increasing melt tension by forming crosslinks between polypropylene molecules has been actively proposed. According to these methods, it is possible to stabilize the cell structure during bubble growth during foaming through intermolecular crosslinking and to improve resistance to thermal collapse. In general, the three-dimensional network structure formed by covalent bonds when crosslinking polyolefin molecules can improve important physical properties such as heat, abrasion, viscous deformation, chemical resistance, etc. and increase impact strength, tensile strength, and the like. At this time, the degree of crosslinking, the distribution of crosslinking, the crosslinking speed and the like all affect the expansion and physical properties of the foam. The crosslinking is influenced by the polyolefin molecular structure and the crosslinking method, time and temperature. Optimum crosslinking is determined by the actual foam expansion experiments of a given process and production. Insufficient crosslinking results in the collapse of bubbles, while excessive crosslinking limits the expansion of the foam.

In the crosslinking method of polypropylene, crosslinking is performed by adding a radical generator, or made of a modified ethylenic resin grafted with an ethylenically unsaturated silane compound, and then in the presence of a radical generator, in the presence of a silanol condensation catalyst and water vapor. So-called crosslinking has been introduced to dramatically improve physical properties such as heat resistance, creep resistance, environmental stress resistance, and chemical resistance. This crosslinking method has industrial value, such as a significant reduction in equipment costs and a relatively easy crosslinking operation, compared to the conventional method using an electron beam. Therefore, the crosslinking method has been applied to wire coating, pipe, film, and shrink tube. have. However, this method is a method of crosslinking the product itself rather than crosslinking the resin itself, and has a disadvantage of requiring a relatively long time when hand-crossing.

As another crosslinking method, the technique of using a polyfunctional monomer as a crosslinking adjuvant is mentioned. In Japanese Patent Application Publication No. 36-6195, organic peroxides and divinylbenzene, In Japanese Patent Publication No. 50-28546, organic peroxides and bismaleimide; In Japanese Patent Publication No. 51-132253, organic peroxides and liquids Polybutene is disclosed in US Pat. No. 3,227,698, which discloses a method for crosslinking polypropylene using organic peroxides and dinitroso compounds, and UK Pat. No. 896,309 using benzoquinone dioximes as crosslinking aids, respectively. All of the polypropylenes by were not commercialized due to insufficient commercial degree of crosslinking.

In contrast, Nojiri et al. Produced a foam by crosslinking polypropylene with triacrylate or trimethacrylate in US Pat. No. 4,424,293. In this method, the crosslinker and polypropylene were kneaded in an extruder, Irradiation of gamma rays to the extruded sheet introduces crosslinking into the polypropylene, but has a disadvantage in that continuous mass production is difficult.

On the other hand, European Patent Nos. 0190889 A2 and 0384431A2 describe a method for producing polypropylene connected by long side chains by irradiating a high energy electron beam to polypropylene in the absence of oxygen. However, this method is limited to the polymorphic amorphous phase, creating long side branches.

Accordingly, the present invention has been made to solve the problems of the prior art, it is an object of the present invention to provide a modified polypropylene resin composition excellent in foamability improved melt tension by the introduction of side branches using a multifunctional monomer.

That is, one aspect of the present invention is 80 to 99 parts by weight of polypropylene having a weight average molecular weight of 300,000 g / mol or more and a melt index of 0.1 to 10 g / 10 minutes (230 ° C.), and a weight average molecular weight of 500,000 g / mol or more. Ethylene having an ethylene / propylene ratio of 50/50 to 90/10 (w / w) with respect to 100 parts by weight of a mixed resin composed of 1 to 20 parts by weight of a high viscosity low density polyethylene having a melt index of 0.1 to 0.5 g / 10 minutes (230 ° C.). It relates to a modified polypropylene resin composition prepared by melt-mixing 0.5 to 10 parts by weight of a propylene block copolymer, 0.05 to 10 parts by weight of a multifunctional monomer and 0.005 to 5 parts by weight of an organic peroxide.

Another aspect of the present invention relates to a foam produced by extruding the modified polypropylene resin composition.

In the present invention, unlike the conventional technique of crosslinking polypropylene molecules to increase the melt tension, it was intended to increase the melt tension by introducing side branches into the polypropylene molecular chain using a polyfunctional monomer in the presence of a radical generator. . In addition, high viscosity low density polyethylene was mixed with polypropylene to maximize foaming properties, and an ethylene-propylene block copolymer was added as a compatibilizer to overcome low compatibility between polypropylene and polyethylene.

Hereinafter, the present invention will be described in more detail.

In the present invention, polypropylene means a block or irregular copolymer of propylene homopolymer or other α-olefin having 2 to 8 carbon atoms. Preferred examples of the α-olefin include 1-butene, 1-pentene, 1-hexene and 1-octene, and copolymerization with propylene. The amount of α-olefin to be produced is 0.001 to 50 mol% per mol of propylene. The weight average molecular weight of the polypropylene is 300,000g / mol or more, the melt index should be 0.1 ~ 10g / 10 minutes (230 ℃).

In the present invention, as described above, a high viscosity low density polyethylene is mixed with the polypropylene, and the reason is that the low density polyethylene has its own side structure and decomposition is different from polypropylene even when radicals are generated by a radical generator. This is because the molecular weight is increased rather than occurring, and the foaming can be expected to be maximized without lowering the overall molecular weight. The high viscosity low density polyethylene used in the present invention is a polyethylene having a weight average molecular weight of 500,000 g / mol or more and a melt index of 0.1 to 0.5 g / 10 minutes (230 ° C.).

According to the present invention, it is preferable to use 1-20 parts by weight of low-density polyethylene by mixing 80 to 99 parts by weight of the polypropylene, and the effect of addition of low-density polyethylene of 1 part by weight or less is insignificant. Causes the heat resistance of the resin composition to decrease.

However, polypropylene and low density polyethylene have poor compatibility despite being the same polyolefin. In the present invention, 0.5 to 10 parts by weight of an ethylene-propylene block copolymer is added as a compatibilizer with respect to 100 parts by weight of the mixture of polypropylene and high viscosity low density polyethylene.

The ethylene-propylene block copolymers used in the present invention are ethylene-propylene copolymers, ethylene-propylene-dicyclo-pentadiene copolymers, ethylene-propylene-1,4-hexadiene rubbers, or ethylene-propylene-cyclo- Pentadiene rubber, it is preferred that the ethylene / propylene ratio is 50/50 ~ 90/10 (w / w).

In the present invention, a conventional organic peroxide is used as the radical generator, preferably di-t-butyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 3-butyl-4,4-bis (t-butyl peroxyvalerate), cumyl hydroperoxide, lauroyl peroxide, t One kind selected from the group consisting of -butyl peroxy acetate, t-butyl peroxy methyl ethyl ketone peroxide, t-butyl cumyl peroxide and (t-butyl peroxy) -butylate is used.

Meanwhile, as the polyfunctional monomer, divinylbenzene, pentaerythritol triacrylate, trimethitol propane triacrylate, 1,6-hexanediol diacrylate, 1,4-butenediol diacrylate, and cyclohexyl methacryl 1 type selected from the group consisting of a rate, methyl acrylate, phenyl acrylate, benzyl acrylate and the like is used.

According to the present invention, the above components are melt mixed in, for example, an extruder and reacted to produce a side chain in the polypropylene molecular chain. In this case, it is preferable to use a twin screw extruder, and the temperature of the extruder is suitably 150 ° C. to 230 ° C., which means that the reaction does not proceed properly when the temperature is too low. This is because the molecular weight of the resin sharply drops.

A foam can be obtained by mixing a conventional volatile blowing agent in the modified polypropylene resin composition of the present invention thus prepared under conditions of high temperature and high pressure, cooling to a suitable foaming temperature, and extruding and foaming under atmospheric pressure.

Preferably, the volatile blowing agent includes aliphatic hydrocarbons such as butane, isobutane, pentane, hexane and heptane; Alicyclic hydrocarbons such as cyclobutane, cyclopentane and cyclohexane; And chlorodifluoromethane, dichloromethane, dichlorofluoromethane, dichlorodifluoromethane, trichlorofluoromethane, chloroethane, dichlorotrifluoroethane, dichlorotetrafluoroethane, trichlorotrifluoroethane, tetrachloro At least one organic gas selected from the group consisting of halogenated hydrocarbons such as difluoroethane and perfluorocyclobutane and / or at least one selected from the group consisting of inorganic gases such as carbon dioxide, nitrogen and air . The addition amount of a blowing agent is selected by the kind of foaming agent, and target foaming ratio, and it is generally suitable that it is 1-20 weight part with respect to 100 weight part of resin compositions. In some cases, a foaming nucleating agent such as sodium bicarbonate-citric acid or talc may be used in combination.

The foam of the present invention prepared as described above preferably has a density of 50 ~ 200kg / cm 3, wherein the cell density is 5E7 ~ 1E10 cells / cm 3.

Hereinafter, the present invention will be described in more detail with reference to examples, but these examples are for illustrative purposes only and should not be construed as limiting the present invention. In the following Examples, the physical property evaluation method is as follows.

[Property evaluation method]

1) Melt Tension

Melt strength of polypropylene was measured using a capillary rheometer manufactured by Toyo Seiki Co., Ltd. (Japan). The polypropylene was held at 230 ° C. for 6 minutes in a barrel and then discharged downward using a piston. At this time, the speed of the piston was 20mm / min and the diameter of the circular die was used was 2.095mm. At the lower end of the capillary rheometer, a pulling device and a device for measuring the pulling force were installed to measure the force while pulling at a constant speed. At this time, the pulling speed was 3.14 m / min.

2) Melt Index

According to ASTM D1238 it was measured to be subjected to a force of 2.16kg at 230 ℃.

3) Density of obtained cylindrical foam and cell density of foam

-Density of foam: It calculated from the weight and the volume calculated | required by the water-immersion method.

Cell density of foam: means the number of cells per cm 3 of foamed resin. Using a scanning electron microscope, the number of cells in a square having a length of 100 μm in one side was calculated and multiplied by the power of 3/2 to calculate the cell density in a cube having a side of 100 μm in one side.

Example 1

90 parts by weight of a polypropylene resin having a melt index of 0.4 g / 10 min (230 ° C., 2.16 kg f) and a ethylene content of 10 wt%, and a high viscosity low density polyethylene 10 having a melt index of 0.3 g / 10 min (230 ° C., 2.16 kg f) 10 3 parts by weight of an ethylene-propylene block copolymer (ethylene content of 60 wt%) in a total of 100 parts by weight of resin mixed with 2,000 ppm of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane as an organic peroxide , 10,000 ppm of polyvinyl divinyl monomer, 1,000 ppm of phenolic antioxidant, 500 ppm of phosphite-based antioxidant, and 700 ppm of calcium stearate as halogen absorber were mixed together, and then melt-blended at 180-230 ° C. with an extruder to pellet It was done. The results of measuring the melt strength by the above method using the pellets are shown in Table 1 below.

The resin pellets obtained above were fed to a 65 mm tandem extruder at 50 kg / h, plasticized at 200 ° C. in a first stage extruder (65 mm), and then 5 parts by weight of isobutane was used as a blowing agent with respect to 100 parts by weight of the resin. After indentation, the resin temperature was cooled to 150 ° C. in a second stage extruder to obtain a strand having a diameter of 5 mm. The physical properties of the foam thus prepared were measured by the above method, and are shown in Table 1 below.

Example 2

100 parts by weight of 90 parts by weight of a homopolypropylene resin having a melt index of 3 g / 10 min (230 ° C., 2.16 kgf) and 10 parts by weight of low density polyethylene having a melt index of 0.3 g / 10 min (230 ° C., 2.16 kgf) 3 parts by weight of an ethylene-propylene block copolymer (ethylene content 60wt%) in resin, 2,000 ppm of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane as an organic peroxide, divinylbenzene as a polyfunctional monomer 10,000 ppm and 1,000 ppm of phenolic antioxidant, 500 ppm of phosphite-based antioxidant, and 700 ppm of calcium stearate as a halogen absorber were mixed together and then pelletized by melt mixing at 180 to 230 ° C. with an extruder. The results of measuring the melt strength by the above method using the pellets are shown in Table 1 below.

After the foam was prepared in the same manner as in Example 1 using the resin pellets obtained above, the physical properties of the foam were measured by the above method and shown in Table 1 below.

Comparative Example 1

100 parts by weight of a polypropylene resin having a melt index of 0.4 g / 10 min (230 ° C., 2.16 kgf), ethylene content of 10% by weight, 1,000 ppm of phenolic antioxidant, 500 ppm of phosphite antioxidant, and calcium as a halogen absorber After mixing 700 ppm stearate together, it was pelletized by melt-mixing at 180-230 degreeC with the extruder. The results of measuring the melt strength by the above method using the pellets are shown in Table 1 below.

After the foam was prepared in the same manner as in Example 1 using the resin pellets obtained above, the physical properties of the foam were measured by the above method and shown in Table 1 below.

Comparative Example 2

After mixing 1000ppm of phenolic antioxidant, 500ppm of phosphite antioxidant, and 700ppm of calcium stearate with halogen absorbent, in 100 parts by weight of homopolypropylene resin having a melt index of 3g / 10min (230 ° C, 2.16kgf) It melted and pelletized at 180-230 degreeC with the extruder. The results of measuring the melt strength by the above method using the pellets are shown in Table 1 below.

After the foam was prepared in the same manner as in Example 1 using the resin pellets obtained above, the physical properties of the foam were measured by the above method and shown in Table 1 below.

Melt Strength and Foaming Result Melt strength (g) Density of foam (g / cc) Cell density of foams (cells / cm 3) Example 1 16.5 0.12 5.5E8 Example 2 12.0 0.15 7.4E8 Comparative Example 1 5.5 0.54 3.4e7 Comparative Example 2 2.0 0.45 2.5E7

As described in detail above, the modified polypropylene resin of the present invention is increased by more than two times the melt tension by the introduction of the side branch to demonstrate excellent foamability in the foaming process, as well as conventional high melt polypropylene resin Unlike the crosslinked structure, the thermoplastic resin is maintained intact, and thus can be recycled.

Claims (10)

80 to 99 parts by weight of polypropylene having a weight average molecular weight of 300,000 g / mol or more and a melt index of 0.1 to 10 g / 10 minutes (230 ° C), and a weight average molecular weight of 500,000 g / mol or more and a melt index of 0.1 to 0.5 g Ethylene-propylene block copolymer 0.5 to 10 having an ethylene / propylene ratio of 50/50 to 90/10 (w / w) per 100 parts by weight of a mixed resin composed of 1 to 20 parts by weight of a high viscosity low density polyethylene that is 10 minutes (230 ° C.). A modified polypropylene resin composition prepared by melt mixing parts by weight, 0.05 to 10 parts by weight of a polyfunctional monomer and 0.005 to 5 parts by weight of an organic peroxide. The modified polypropylene resin composition according to claim 1, wherein the polypropylene is homopolypropylene. The polypropylene is a block or irregular copolymer of propylene with another α-olefin having 2 to 8 carbon atoms, and the amount of α-olefin copolymerized with propylene is 0.001 to 50 mol% per mol of propylene. Modified polypropylene resin composition, characterized in that. The modified polypropylene resin composition according to claim 3, wherein the α-olefin is one selected from the group consisting of 1-butene, 1-pentene, 1-hexene and 1-octene. The ethylene-propylene block copolymer according to claim 1, wherein the ethylene-propylene block copolymer is an ethylene-propylene copolymer, an ethylene-propylene-dicyclo-pentadiene copolymer, ethylene-propylene-1,4-hexadiene rubber and ethylene-propylene-cyclo- A modified polypropylene resin composition, characterized in that one kind selected from the group consisting of pentadiene rubber. The method of claim 1, wherein the polyfunctional monomer is divinylbenzene, pentaerythritol triacrylate, trimethitol propane triacrylate, 1,6-hexanediol diacrylate, 1,4-butenediol diacrylate, Modified polypropylene resin composition, characterized in that one kind selected from the group consisting of cyclohexyl methacrylate, methyl acrylate, phenyl acrylate and benzyl acrylate. The method of claim 1, wherein the organic peroxide is di-t-butyl peroxide, dicumylperoxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2, 5-di (t-butylperoxy) hexane, 3-butyl-4,4-bis (t-butyl peroxyvalerate), cumylhydroperoxide, lauroyl peroxide, t-butylperoxyacetate, t- Modified polypropylene resin composition, characterized in that it is one kind selected from the group consisting of butyl peroxymethyl ethyl ketone peroxide, t-butyl cumyl peroxide and (t-butyl peroxy) -butylate. The modified polypropylene resin composition according to claim 1, wherein the melt mixing is performed at a temperature of 150 to 230 ° C. 1 to 20 parts by weight of a volatile blowing agent is mixed under high temperature and high pressure conditions with respect to 100 parts by weight of the modified polypropylene resin composition prepared according to any one of claims 1 to 8, and cooled to a suitable foaming temperature, followed by atmospheric pressure. A foam having a density of 50 to 200 kg / cm 3 and a cell density of 5E7 to 1E10 cells / cm 3, prepared by extrusion foaming under. 10. The foam according to claim 9, wherein the volatile blowing agent is at least one organic gas selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons and halogenated hydrocarbons, and / or at least one inorganic gas.