JP3564264B2 - Buffer material made of new polypropylene resin foam - Google Patents

Description

【００３３】
【表２】

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a novel cushioning material having excellent heat resistance and high cushioning properties even at a low density.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, when transporting a product that is vulnerable to an external impact such as an electric product or an electronic component, various so-called cushioning materials have been used to reduce the impact and protect the product from damage.
Above all, foamed plastic is a cushioning material that is used most often because of its excellent properties of absorbing shock and absorbing shock applied to products (so-called cushioning property). The level of cushioning of the foamed plastic depends on the type of plastic making up the foam. The most frequently used foams made of polystyrene have a drawback that, due to the lack of flexibility of polystyrene, repeated impacts cause the foam to be destroyed and the cushioning property to be rapidly reduced. On the other hand, the cushioning material made of the foamed polyethylene resin does not decrease the buffering property against the repeated impact as described above because the polyethylene resin is rich in flexibility, but the foaming because the elastic modulus of the polyethylene resin is low. When the magnification is increased, the compressive strength of the foam decreases, and the cushioning property decreases. Therefore, a low-density cushioning material cannot provide a sufficient level of cushioning.
[0003]
On the other hand, a foam made of a polypropylene-based resin is expected to have excellent elasticity even at a lower density than a polyethylene-based resin because it has a higher elastic modulus than a polyethylene-based resin. However, it is extremely difficult to form a normal polypropylene-based resin into a foam. That is, in the case of polyethylene-based resin, the resin is melted in an extruder, and a foaming agent is pressed and melted under high pressure and extruded into a low-pressure region, and a thick plate-like foam having a thickness of 30 mm to 100 mm is formed. It is easy to cut out this and use it as a cushioning material. On the other hand, in the case of a polypropylene-based resin, since a foam cannot be obtained by such a method at all, a plate-like foam that can be used as a cushioning material is obtained. Has not been obtained yet.
[0004]
Using a polypropylene resin, the buffer material is used as a buffer, impregnated with a foaming agent under high pressure in a dispersion medium such as water, and spouted rapidly from the orifice into the low pressure region. There is only a molded product (that is, a molded product of pre-expanded particles) obtained by a method in which expanded particles are filled in a mold, heated with steam or the like, and molded. Such a cushioning material exhibits excellent cushioning properties even at a low density, but has a problem in that the production cost is high due to its specialty in the production method.
[0005]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to find a novel cushioning material which is easy to manufacture, low in cost, and can exhibit high cushioning properties even at low density.
[0006]
[Means for Solving the Problems]
Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a foam made of a polypropylene-based resin modified by a specific method satisfies the above object, and have reached the present invention.
That is, the present invention relates to a cushioning material comprising a foam of a modified polypropylene resin obtained by melt-kneading a polypropylene resin, an isoprene monomer, and a radical generator.
[0007]
Further, the polypropylene resin is preferably a resin selected from the group consisting of homopolypropylene and a copolymer of propylene and ethylene and / or an α-olefin containing a propylene component of 80% by weight or more.
Further, the present invention comprises a modified polypropylene resin obtained by melt-kneading a polypropylene resin, an isoprene monomer, and a radical generator, and has a density of 9 to 30 kg / m ³ and a minimum thickness of 30 mm or more. The present invention relates to a cushioning material made of a foam.
[0008]
Further, the present invention relates to a cushioning material comprising the foam obtained by the extrusion foaming method.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, it is important to use modified PP under specific conditions. That is, it is essential to use a modified polypropylene obtained by melt-kneading a polypropylene resin, an isoprene monomer and a radical generator. It is not known at all that the use of such a modified polypropylene makes it possible to obtain a novel cushioning material that can exhibit high cushioning properties even at a low cost at a low cost. It was not.
[0010]
The method of producing the cushioning material using such a specific modified polypropylene is optional, and the above-mentioned pre-expanded particles can be used. It can also be a foam. In terms of cost, the latter is advantageous.
A method for producing a modified polypropylene obtained by melt-kneading a polypropylene resin, an isoprene monomer and a radical generator, which are essential requirements of the present invention, will be described.
[0011]
In the present invention, as the polypropylene-based resin before melt-kneading, a resin generally called a polypropylene-based resin can be used, and the use within the range is not limited. And a random or block copolymer of propylene and an α-olefin other than ethylene are preferred.
[0012]
When the polypropylene resin before the modification is a copolymer of propylene and ethylene or other α-olefin, the propylene monomer component contained therein is reduced from the viewpoint of exhibiting high buffering properties at a low density. It is preferably at least 80% by weight, more preferably at least 90% by weight.
The melt index of the polypropylene resin before modification is preferably in the range of 0.1 to 10.
The amount of the isoprene monomer to be added is preferably 0.1 to 20 parts by weight based on 100 parts by weight of the polypropylene resin. More preferably, the total amount of the monomers is 0.5 to 5 parts by weight. If the addition amount is less than the above range, the effect of improving foamability tends to be insufficient, while if it is more than the above range, a large amount of unreacted monomer remains or a large amount of a polymer that does not graft exists. Tends to lower the properties of the foam.
[0013]
In the present invention, a small amount of an aromatic vinyl monomer may be used in combination with isoprene. Examples of the aromatic vinyl monomer include styrene; methylstyrene such as o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, β-methylstyrene, dimethylstyrene, and trimethylstyrene; -Chlorostyrene such as -chlorostyrene, β-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, dichlorostyrene, and trichlorostyrene; o-bromostyrene, m-bromostyrene, p-bromostyrene, dibromo Bromostyrene such as styrene and tribromostyrene; fluorostyrene such as o-fluorostyrene, m-fluorostyrene, p-fluorostyrene, difluorostyrene and trifluorostyrene; o-nitrostyrene, m-nitrostyrene and p-nitrostyrene Nitrostyrenes such as styrene, dinitrostyrene and trinitrostyrene; vinylphenols such as o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, dihydroxystyrene and trihydroxystyrene; o-divinylbenzene, m-divinylbenzene, p Divinylbenzene such as -divinylbenzene; and one or more kinds of isopropenylstyrene such as o-diisopropenylbenzene, m-diisopropenylbenzene and p-diisopropenylbenzene.
[0014]
When the aromatic vinyl monomer is used in combination, the amount added is preferably less than 100 parts with respect to 100 parts of the isoprene monomer, from the viewpoint of maintaining the high buffering property which is the object of the present invention.
The radical generator generally includes a peroxide or an azo compound.
[0015]
Specific examples of the radical generator include ketone peroxides such as methyl ethyl ketone peroxide and methyl acetoacetate peroxide; 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, Peroxy ketals such as, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate and 2,2-bis (t-butylperoxy) butane; Hydroperoxides such as permethane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide; dicumyl peroxide, 2,5-dimethyl-2, 5-di (t-butylperoxy) Xane, α, α'-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di (t- Dialkyl peroxides such as butylperoxy) hexine-3; diacyl peroxides such as benzoyl peroxide; di (3-methyl-3-methoxybutyl) peroxydicarbonate and di-2-methoxybutylperoxydicarbonate. Peroxydicarbonate; t-butylperoxyoctate, t-butylperoxyisobutyrate, t-butylperoxylaurate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butyl Peroxyisopropyl carbonate, 2,5-dimethyl-2,5-di (ben Irupaokishi) hexane, t- butyl peroxy acetate, t- butyl peroxybenzoate, organic peroxides such as peroxy esters such as di -t- butyl peroxy isophthalate and the like.
[0016]
The amount of the radical generator added is 0.01 to 100 parts by weight of the polypropylene resin before modification, since the melt viscosity of the modified polypropylene resin does not excessively decrease and is economical. It is preferably in the range of from 5 to 5 parts by weight, more preferably in the range of from 0.1 to 1 part by weight.
If the amount of the radical generator is less than the above range, the modifying effect tends not to be sufficiently obtained, while if it is more than the above range, a foam having a suitable shape and appearance is obtained. Tend not to be.
[0017]
If necessary, other resins or rubbers other than the polypropylene-based resin may be added to the polypropylene-based resin before modification, as long as the effects of the present invention are not impaired. Other resins or rubbers other than the polypropylene resin include, for example, polyethylene; polyα-olefins such as polybutene-1, polyisobutene, polypentene-1, and polymethylpentene-1; ethylene / propylene having a propylene content of less than 75% by weight. Ethylene or α-olefin / α-olefin copolymers such as copolymers, ethylene / butene-1 copolymers, propylene / butene-1 copolymers having a propylene content of less than 75% by weight; Less than wt% ethylene or α-olefin / α-olefin / diene monomer copolymer such as ethylene / propylene / 5-ethylidene-2-norbornene copolymer; ethylene / vinyl chloride copolymer, ethylene / chloride Vinylidene copolymer, ethylene / acrylonitrile copolymer, ethyl Len / methacrylonitrile copolymer, ethylene / vinyl acetate copolymer, ethylene / acrylamide copolymer, ethylene / methacrylamide copolymer, ethylene / acrylic acid copolymer, ethylene / methacrylic acid copolymer, ethylene / Maleic acid copolymer, ethylene / ethyl acrylate copolymer, ethylene / butyl acrylate copolymer, ethylene / methyl methacrylate copolymer, ethylene / maleic anhydride copolymer, ethylene / metal acrylate copolymer Ethylene or α-olefin / vinyl monomer copolymers such as a copolymer, an ethylene / methacrylic acid metal salt copolymer, an ethylene / styrene copolymer, an ethylene / methylstyrene copolymer, and an ethylene / divinylbenzene copolymer; Polydiene-based copolymers such as polyisobutene, polybutadiene, and polyisoprene Vinyl monomer such as styrene / butadiene random copolymer / diene monomer random copolymer; vinyl monomer such as styrene / butadiene / styrene block copolymer / diene monomer / vinyl monomer Block copolymer; hydrogenation (vinyl monomer / diene monomer random copolymer) such as hydrogenation (styrene / butadiene random copolymer); hydrogenation (styrene / butadiene / styrene block copolymer) (Vinyl monomer / diene monomer / vinyl monomer block copolymer); vinyl such as acrylonitrile / butadiene / styrene copolymer, methyl methacrylate / butadiene / styrene copolymer Monomer / diene monomer / vinyl monomer graft copolymer; polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, Vinyl polymers such as vinyl acetate, polyethyl acrylate, polybutyl acrylate, and polymethyl methacrylate; vinyl chloride / acrylonitrile copolymer, vinyl chloride / vinyl acetate copolymer, acrylonitrile / styrene copolymer, methacrylic acid And vinyl copolymers such as methyl / styrene copolymer.
[0018]
The amount of these other resins or rubbers to be added to the polypropylene resin before the modification differs depending on the type of the resin or the type of the rubber, and may be within the range that does not impair the effects of the present invention as described above. It is preferable that the content is not more than about% by weight.
Further, if necessary, an antioxidant, a metal deactivator, a phosphorus-based processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, a fluorescent brightener, a metal soap, an antacid Additives such as stabilizers or cross-linking agents such as adsorbents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing materials, pigments, dyes, flame retardants, and antistatic agents do not impair the effects of the present invention. You may add in the range.
[0019]
The temperature condition for melt-kneading the polypropylene resin, the isoprene monomer and the radical generator is a temperature at which the polypropylene resin melts, and can be arbitrarily selected within a temperature range at which the radical generator can be decomposed. . Preferably, it is in the range of 130 ° C to 250 ° C. The time for melt-kneading is generally 1 to 60 minutes.
[0020]
Examples of the melt kneading apparatus include roll, co-kneader, Banbury mixer, Brabender, kneading machines such as a single-screw extruder or a twin-screw extruder, and horizontal stirring machines such as a twin-screw renewer or a twin-screw multi-disc device. Alternatively, there is a device such as a vertical stirrer such as a double helical ribbon stirrer which can heat a polymer material to an appropriate temperature and knead it while giving an appropriate shear stress. Of these, extruders are particularly preferred in terms of productivity. Further, the melt-kneading may be repeated a plurality of times in order to sufficiently uniformly mix the respective materials.
A method for producing a foam suitable for a cushioning material using a propylene-based resin will be described.
[0021]
As an example of a method for producing a foam made of the modified polypropylene resin of the present invention, (1) the foaming agent is pressed into a molten modified polypropylene resin, melted, and then extruded by a melt extruder. (2) forming the modified polypropylene-based resin into particles, dissolving a foaming agent in the modified polypropylene-based resin particles in a pressure vessel or in an aqueous suspension; Dispersed, then depressurized foaming, that is, the modified polypropylene-based resin particles in which the foaming agent is dissolved or dispersed are kept under pressure, and then foamed by releasing them in a low-pressure atmosphere, and the A method of producing expanded particles, and forming the pre-expanded particles into a foamed molded article by a method such as molding in a mold may be used.
[0022]
In the present invention, as described above, since the production cost is low, the foaming agent is pressed into the melted modified polypropylene resin of (1) and melted, and then melt-extruded. A method of obtaining a foam by extruding with a machine is preferable, and this method is described in detail.
As the foaming agent in the present method, a foaming agent usually used in an extrusion foaming method can be used, and among them, a hydrocarbon-based foaming agent such as propane, butane, and pentane is preferable.
[0023]
The injection amount of the blowing agent may be selected depending on the type of the blowing agent and the target expansion ratio, but is preferably in the range of usually 2 to 30 parts by weight based on 100 parts by weight of the modified polypropylene resin.
If necessary, a foam nucleating agent such as sodium bicarbonate-citric acid or talc may be used in combination in order to control the cell diameter of the foam to an appropriate size. Usually, the amount of the foaming nucleating agent used as needed is preferably 0.001 to 2 parts by weight based on 100 parts by weight of the modified polypropylene resin.
[0024]
The modified polypropylene resin is melted in an extruder, the blowing agent is press-fitted into the extruder, and kneaded with the modified polypropylene resin in a molten state while maintaining a high pressure, and the fully kneaded modified polypropylene is mixed. By discharging a kneaded body of the base resin and the volatile foaming agent from a die, the foamed body can be formed. The melt-kneading temperature and the melt-kneading time in this method may be appropriately selected depending on the foaming agent used and the kneading conditions, and vary depending on the type of the resin, but the melt-kneading temperature is 130 to 300 ° C., and the melt-kneading time is 1 to 120 minutes. Is usually
[0025]
The density of the foam in the present invention is preferably 9 to ³⁰ kg / m ³ in order to exhibit the features of light weight and excellent cushioning properties.
The width of the foam of the present invention is arbitrary, but generally ranges from 300 mm to 1000 mm.
According to the present invention, a plate-like foam having a thickness of 30 mm or more can be easily obtained, and has excellent repetitive buffer characteristics required as a buffer material.
[0026]
In addition, the foam of the present invention preferably has a closed cell ratio of 50% or more, and more preferably 80% or more, from the viewpoint of high buffering properties.
As the cushioning material of the present invention, the above-mentioned plate-shaped foam can be used as it is, or can be used by cutting out or laminating it to a required shape.
[0027]
【Example】
Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited to only these examples.
The density, closed cell ratio, and appearance of the foam were evaluated by the following methods.
(Foam density)
It was calculated from the weight and the volume determined by the submersion method.
(Closed cell rate)
The measurement was carried out using a multipycnometer (manufactured by Yuasa Ionics Co., Ltd.) according to the method A of ASTM D-2856.
(appearance)
By the visual observation of the foam surface, it was classified into ○: no unfoamed portion, burrs and wrinkles were observed, and ×: unfoamed portion, burrs and wrinkles were observed.
[0028]
Embodiment 1
100 parts by weight of an ethylene propylene random copolymer (manufactured by Grand Polymer Co., Ltd., Hypol B230, ethylene content: 3% by weight, melt flow index at 230 ° C .: 0.5 g / 10 minutes) and 2.5 parts by weight of isoprene monomer And 0.5 parts by weight of 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane (manufactured by NOF CORPORATION, Perhexa 3M, half-life at 147 ° C. for 1 minute) in 200 parts by weight. C. (160 ° C. only at the bottom of the hopper) is supplied to a 44 mm twin-screw extruder (L / D = 32), where the resin is melted and kneaded at a screw rotation speed of 200 rpm, and the resin is mixed and reacted to obtain a modified polypropylene. A polymer was obtained.
[0029]
To 100 parts by weight of the obtained modified polypropylene polymer, 0.02 parts by weight of a blended oil and 0.02 parts by weight of sodium bicarbonate-citric acid as a foam nucleating agent were mixed using a ribbon blender. This mixture was supplied to a 115 mm-150 mm tandem type extruder, and after being plasticized at 230 ° C. in a first stage extruder (115 mm), isobutane as a foaming agent was added to 100 parts by weight of the modified polypropylene-based polymer. 14 parts by weight, and cooled in a second-stage extruder (150 mm) so that the resin temperature becomes 135 ° C., and extruded from a slit die (width 120 mm × thickness 6 mm), 600 mm wide and 50 mm thick. A plate-like foam was obtained. The density of the obtained foam was 23 kg / m ³ and the closed cell ratio was 90%. The cushioning property of this product was superior to that of a polyethylene foam having a density of 30 kg / m ³ . In addition, even if the impact was repeatedly applied, a decrease in the buffering property was hardly observed.
[0030]
[Examples 2 to 5]
Modification of polypropylene and extrusion foaming were performed in the same manner as in Example 1 except that the mixing ratio of the raw materials when supplied to the twin-screw extruder was changed as shown in Table 1. Table 2 shows the properties of the obtained foam. These cushioning properties were superior to polyethylene foams having a density of 30 kg / m ³ . In addition, even if the impact was repeatedly applied, a decrease in the buffering property was hardly observed.
[0031]
[Comparative Examples 1-3]
Table 2 shows the results of preparing plate-like foams of polyethylene and polystyrene, and evaluating the buffering property and the buffering property after repeatedly applying impact.
[0032]
[Table 1]

[0033]
[Table 2]

Claims (4)

A buffer comprising a foam of a modified polypropylene resin obtained by melt-kneading a polypropylene resin, an isoprene monomer, and a radical generator. The buffer material according to claim 1, wherein the polypropylene resin is selected from the group consisting of homopolypropylene and a copolymer of propylene and ethylene and / or an α-olefin containing a propylene component of 80% by weight or more. A buffer material made of a modified polypropylene resin obtained by melt-kneading a polypropylene resin, an isoprene monomer, and a radical generator, and having a density of 9 to 30 kg / m ³ and a minimum thickness of 30 mm or more. . The cushioning material according to claim 1, wherein the foam is a foam obtained by an extrusion foaming method.