JP2008120979A - Polypropylenic resin foam sheet and formed article comprising the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylenic resin foam sheet which has a density range suitable for use in cushioning package materials of 0.07-0.6 g/ml, and fine and closed cells and exhibits sufficient antistatic characteristics. <P>SOLUTION: The polypropylenic resin foam sheet is prepared by extrusion-foaming a resin composition consisting of (a) a polypropylenic resin having a specific zero-shear viscosity η<SB>0</SB>and a complex viscosity η* and (b) a high molecular weight ant-static agent and forming the resultant resin composition foam having a density of 0.07-0.6 g/ml and a closed cell ratio of ≥60% into a sheet. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polypropylene resin foam sheet having antistatic properties and a molded product thereof. In particular, as well as showing good antistatic performance, the cell has a fine and high closed cell ratio, so that it can be used as a food container or various buffer packaging materials, or as a buffer material when transporting electronic components that dislike surface charging. The present invention relates to a polypropylene resin foam sheet and a molded body thereof that are particularly preferably used as a partition material, a return tray, and the like.

  Polypropylene-based resin foam sheets are conventionally used as food containers and buffer packaging materials because they are excellent in rigidity, heat resistance, chemical resistance, buffering properties, and the like. However, the polypropylene resin is easily charged due to its high chargeability, and static electricity accumulated on the surface may be a problem when used as an electronic component container.

  Then, the proposal which raises the antistatic performance of a polypropylene resin foam sheet using an antistatic agent is made | formed. Specifically, a method of applying a surfactant type antistatic agent to the surface of the foamed sheet or a method of kneading into the foamed sheet has been used.

  However, since the surfactant type antistatic agent has a low molecular weight, there is an undesirable problem that the surface becomes sticky or migrates to the surface of the object to be packaged and becomes fouled. In addition, in applications such as electronic parts containers, the surface may be washed repeatedly and used repeatedly. In the case of a surfactant type antistatic agent, it is lost from the surface by washing with water and does not exhibit a predetermined antistatic performance. There was a problem that there was something.

  On the other hand, the proposal which tries to solve problems, such as surface stickiness and the surface contamination of the to-be-packaged object, is made | formed by using a polymeric antistatic agent (patent document 1).

  In Patent Document 1, a resin composition obtained by adding a polymer type antistatic agent having a specific crystallization temperature and a melt viscosity at a specific ratio to a polyolefin resin (including a polypropylene resin). A method for producing a polyolefin resin foam having a specific density range obtained by extrusion foaming is disclosed.

  However, in order to exhibit sufficient antistatic performance by this method, the density range of the polyolefin resin foam needs to be 65 g / L (0.065 g / ml) or less. When it is intended to obtain a foam having a density range of 0.07 to 0.6 g / ml, which is suitably used in cushioning packaging materials as a molded product that is thermoformed into, etc., the antistatic performance is not sufficiently developed. There was a problem.

  Conversely, when the amount of the polymeric antistatic agent is increased to increase the antistatic performance, the bubble diameter becomes coarse and the appearance deteriorates, and the closed cell ratio also tends to decrease, and the buffer performance decreases. As a result, there is a problem that the commercial value is remarkably impaired.

As described above, the present situation is that a polypropylene resin foam sheet having a specific density range suitable as a buffer packaging material has not been obtained because the cells are fine and the closed cell ratio is high while exhibiting sufficient antistatic performance.
JP 2005-194433 A

  An object of the present invention is to provide a polypropylene resin foam sheet having a specific density range suitable as a buffer packaging material, having fine cells and closed cells, and further exhibiting sufficient antistatic performance. It is.

  In view of the above-mentioned problems of the prior art, the present inventors use a polypropylene resin exhibiting specific viscoelastic properties as a base resin, so that even if the addition amount of the polymer antistatic agent is increased, the cell roughness is increased. As a result, it was found that the reduction of the ratio and the reduction of the closed cell ratio can be greatly suppressed, and the present invention has been completed.

That is, the present invention
100 parts by weight of a polypropylene resin (a) having a zero shear viscosity η ₀ at 210 ° C. and a complex viscosity η ^* at a frequency of 100 (/ sec) at 210 ° C. satisfying the following expressions (1) and (2): A density of 0.07 to 0.6 g / ml and a closed cell ratio of 60% or more obtained by extrusion foaming a resin composition comprising more than 2 parts by weight and not more than 25 parts by weight of a high molecular weight antistatic agent (b) A polypropylene resin foam sheet (Claim 1),

The polypropylene resin foam sheet (Claim 2) according to claim 1, wherein the resin composition contains a polymer-type antistatic agent (b) in an amount of more than 8 parts by weight and 25 parts by weight or less.
The polypropylene-based resin foam sheet according to claim 1 or 2, wherein the closed cell ratio is 70% or more (claim 3),
The polypropylene-based resin foam sheet according to any one of claims 1 to 3, wherein an average cell diameter in the sheet thickness direction is 0.05 mm or more and less than 0.4 mm (Claim 5).
The polypropylene-based resin foam sheet according to any one of claims 1 to 3 (claim 6) and any one of claims 1 to 4, wherein an average cell diameter in the sheet thickness direction is 0.1 mm or more and less than 0.2 mm. A molded product obtained by thermoforming the polypropylene resin foam sheet according to claim 7 (Claim 7).
About.

  According to the present invention, for example, a polypropylene-based resin having a density range of 0.07 to 0.6 g / ml which is preferably used in buffer packaging materials as a sheet or as a molded product thermoformed on a tray or the like Even if it is a foam sheet, a polypropylene resin foam sheet having excellent antistatic performance, excellent buffer performance due to its high closed cell ratio, and excellent appearance due to its fine cell diameter, A molded product obtained by thermoforming the foamed sheet can be obtained.

The polypropylene resin foam sheet of the present invention is obtained by extrusion foaming a resin composition comprising a polypropylene resin (a) having a specific zero shear viscosity η ₀ and complex viscosity η ^* and a polymer antistatic agent (b). Are manufactured.

The polypropylene resin (a) in the present invention has a zero shear viscosity η _{0 at} 210 ° C. that satisfies the following formula (1).

The zero shear viscosity η ₀ is an index of shear viscosity when the shear rate is very small. By setting η ₀ within this range, even if an amount of a polymer type antistatic agent necessary for exhibiting sufficient antistatic performance is added, the closed cell ratio of 0.07 to 0.6 g / ml can be obtained. A high polypropylene resin foam sheet can be obtained easily.

The polypropylene resin composition (a) of the present invention preferably has a zero shear viscosity ηo at 210 ° C. of 1 × 10 ⁵ ≦ ηo (Pa · sec) ≦ 5 × 10 ⁵ , and 1.2 × 10 ⁵ ≦ ηo ( Pa · sec) ≦ 4.5 × 10 ⁵ is more preferable, and 1.5 × 10 ⁵ ≦ ηo (Pa · sec) ≦ 4 × 10 ⁵ is more preferable.

When the zero-shear viscosity η ₀ at 210 ° C. of the polypropylene resin (a) is less than 1 × 10 ⁵ Pa · sec, the closed cell ratio of the foam sheet tends to decrease with the addition of the polymer antistatic agent. There is a tendency. Moreover, when the polypropylene resin foam sheet of the present invention is molded by thermoforming or the like, the drawdown of the foam sheet becomes large, and it tends to be difficult to obtain a good molded product.

When η _{0 of the} polypropylene resin (a) exceeds 5 × 10 ⁵ Pa · sec, the resin temperature tends to be high in the melt-kneading step of the resin composition used for obtaining the foamed sheet of the present invention, and the resin temperature is appropriately set. It tends to be insufficient for cooling to maintain the temperature.

Furthermore, the polypropylene resin (a) satisfies the following formula (2) in terms of complex viscosity η ^* at a frequency of 100 (/ sec) at 210 ° C.

The complex viscosity η ^* is an index of shear viscosity when the shear rate is relatively high. By setting the complex viscosity η ^* within the above range, the polypropylene resin (a) and the polymer antistatic agent (b) are uniformly mixed, and sufficient antistatic performance can be obtained with a relatively small amount of antistatic agent added. The polypropylene resin foam sheet shown can be obtained.

When the complex viscosity η ^* of the polypropylene resin (a) is less than 400 Pa · sec, the polypropylene resin (a) and the polymer antistatic agent are difficult to be mixed uniformly, and the polymer for exerting antistatic performance The added amount of the mold antistatic agent is increased, and as a result, the closed cell ratio of the obtained foamed sheet tends to decrease.

On the other hand, there is no upper limit for η ^* of the polypropylene resin (a), but it is usually preferably 600 Pa · sec or less. When η ^* exceeds 600 Pa · sec, the surface smoothness of the foamed sheet is deteriorated and the merchantability tends to be impaired.

The zero-shear viscosity η ₀ and the complex viscosity η ^{* at} a frequency of 100 (/ sec) of the polypropylene resin (a) of the present invention are values calculated by measuring as follows.

In both measurements, the target resin is molded into a flat plate shape using a press machine adjusted to 190 ° C., and punched to a diameter of 25 mm with a punch, and used as a measurement sample.
As a device, Rheometric Scientific F.M. E. A SR-2000, a rheometer made by the company, is used. The measurement conditions are 210 ± 1 ° C., with nitrogen gas flowing in the measurement system.

The zero shear viscosity η ₀ is measured by sandwiching the sample between 25 mm diameter parallel plates, adjusting the gap between the two plates to 1.4 ± 0.05 mm, excluding the sample resin protruding from the plate, and letting it stand for 20 minutes. After placing, a stress of 100 Pa is applied for 300 seconds, and the creep compliance J (t) with respect to time t is recorded.
The zero shear viscosity η ₀ is calculated as the reciprocal of the slope of the approximate straight line in the part where J (t) can be regarded as a straight line with respect to t, but in actuality, the attached control program RSI Orchestrator Ver. Calculated using the function in 6.3.2.

The complex viscosity η ^* is measured by putting the sample in a cone plate with a diameter of 25 mm, adjusting the gap between the two plates to 0.05 ± 0.005 mm, excluding the sample resin protruding from the plate, and allowing to stand for 20 minutes. After that, the attached control program RSI Orchestrator Ver. The complex viscosity η ^* is measured in the frequency range of 10 to 100 (/ sec) under the stress condition of 100 Pa by the test in the Dynamic Frequency Sweep Test (Stress Control) mode, which is one of the test modes of 6.3.2. To do. At this time, the value of η ^* at 100 (/ sec) was adopted as the complex viscosity η ^* at a frequency of 100 (/ sec) at 210 ° C.

In the case where the polypropylene resin (a) is a mixture composed of a plurality of components, η ₀ and η ^* are measured for each component, and the polypropylene resin (a) of the following formulas (3) and (4) is measured. η ₀ and η ^* are calculated.

<In formula, η _0a : Zero shear viscosity of polypropylene resin (a), w _n : Weight fraction of component n contained in polypropylene resin (a) (w ₁ + w ₂ +... + W _n = 1 ), Η _0n : Zero shear viscosity of component n>

<Wherein, η ^* _a: complex viscosity at vibration frequency 100 (/ sec) of the polypropylene resin (a), w _n: weight fraction of component n contained in the polypropylene resin _{(a) (w 1 + w} 2 + ... + W _n = 1), η ^* _n : complex viscosity at frequency 100 (/ sec) of component n>

  The method for obtaining the polypropylene resin (a) of the present invention is not particularly limited. For example, as an example of a preferred embodiment, a polypropylene resin (hereinafter also referred to as “raw resin”), radical polymerization, Examples thereof include a method in which a modified polypropylene resin obtained by melt-kneading a functional monomer and a radical polymerization initiator is used as a polypropylene resin (a) or as a part of the polypropylene resin (a).

  Specific methods for obtaining the modified polypropylene resin include, for example, (1) a polypropylene resin, an aromatic vinyl monomer, and a radical polymerization initiator described in JP-A-9-188728. (2) A method of melt-kneading a polypropylene resin, an isoprene monomer and a radical polymerization initiator, as described in JP-A-9-188729, (3) JP-A-9-278836 The method of melt-kneading a polypropylene-based resin, a 1,3-butadiene monomer, and a radical polymerization initiator, etc., described in Japanese Patent Publication No. H.

Furthermore, means for setting the zero shear viscosity η ₀ and the complex viscosity η ^* within the scope of the present invention will be described in detail.

In the method of melt-kneading a polypropylene resin, a radical polymerizable monomer and a radical polymerization initiator, it is considered that the crosslinking reaction between the main chains of the raw material resin and the main chain cleavage reaction proceed simultaneously. Η ₀ and η ^* change depending on the degree of progress of. Therefore, in order to obtain a target modified polypropylene resin, the melt flow rate of the raw material resin (hereinafter sometimes referred to as “MFR”) and the combination of the radical polymerizable monomer and the radical polymerization initiator with respect to the raw material resin It is necessary to adjust the amount.

Specifically, η ₀ can be adjusted by the MFR of the raw material resin, the blending amount of the radical polymerization initiator, and the blending ratio of the radical polymerizable monomer to the radical polymerization initiator.
Generally, when the MFR of the raw material resin is small, η _{0 of the} modified polypropylene resin tends to increase. When the amount of the radical polymerization initiator is large, η ₀ tends to increase. When the blending ratio of the radical polymerizable monomer to the radical polymerization initiator is large, η ₀ tends to increase.

Further, η ^* can also be adjusted by the MFR of the raw material resin, the blending amount of the radical polymerization initiator, and the blending ratio of the radical polymerizable monomer to the radical polymerization initiator.
Generally, when the MFR of the raw material resin is small, η ^{* of the} modified polypropylene resin tends to increase. When the amount of the radical polymerization initiator is large, η ^* tends to be small. When the blending ratio of the radical polymerizable monomer to the radical polymerization initiator is large, η ^* tends to increase.

  When the modified polypropylene resin is used as the polypropylene resin (a), the raw material resin is a melt flow rate (“MFR”) measured under the condition of 2.16 kg load at 230 ° C. according to the measurement method of JIS K7210. It is preferable to use a polypropylene resin in the range of 1.0 to 5.0 g / 10 min.

When the MFR of the raw material resin is less than 1.0, the zero shear viscosity η ₀ tends to be large, and a gel-like product tends to be easily formed in the obtained resin. When MFR exceeds 5.0, a large amount of necessary radical polymerization initiators and radical polymerizable monomers are required, which tends to impair economic efficiency.

In order to obtain the polypropylene-based resin (a) of the present invention, a preferable blending amount of the radical polymerization initiator varies depending on the kind of the radical polymerization initiator to be used, but is generally 0.2 to 1 with respect to 100 parts by weight of the raw material resin. 0.5 parts by weight, more preferably in the range of 0.3 to 1.0 parts by weight. When the blending amount of the radical polymerization initiator is less than 0.2 parts by weight, the crosslinking reaction does not proceed sufficiently, and η ₀ tends to be difficult to be within the scope of the present invention. When the blending amount is larger than 1.5 parts by weight, the crosslinking reaction proceeds too much, and η ₀ tends to be excessively increased.

In order to obtain the polypropylene-based resin (a) of the present invention, the blending ratio of the radical polymerizable monomer to the preferred radical polymerization initiator varies depending on the type of the radical polymerization initiator and the radical polymerizable monomer, but is generally about weight. The ratio is in the range of 1.0 to 2.5, more preferably 1.3 to 2.0. When the blending ratio is smaller than 1.0, the cleavage reaction occurs preferentially, and it tends to be difficult to make η ₀ within the target range. On the other hand, when the blending ratio is larger than 2.5, a crosslinking reaction occurs preferentially and the zero shear viscosity η ₀ tends to be excessively increased.

In the present invention, when the modified polypropylene resin is used as a part of the polypropylene resin (a), the polypropylene resin (a) is selected from the group consisting of the modified polypropylene resin and the following other resins and rubbers. And at least one kind.
At this time, the propylene monomer contained in the polypropylene resin (a) is 75% by weight or more of the total from the viewpoint of maintaining the high rigidity, chemical resistance, and heat resistance that are the characteristics of the polypropylene resin. Preferably, it is more preferably 90% by weight or more of the whole. However, the polypropylene-based resin (a) may be a pellet or a mixture of powders constituting the component, or may be a pellet obtained by once melting and kneading each component.

  Preferred examples of the other resin and rubber include propylene homopolymers and copolymers of propylene and other monomers. When the other resin or rubber is a copolymer of propylene and another monomer, examples of a preferably used monomer include ethylene, butene-1, hexene-1, octene-1, and the like. α-olefin, cyclic olefin, diisopropenylbenzene; diene monomers such as isoprene, 1,3-butadiene, chloroprene, styrene, methylstyrene, chlorostyrene, bromostyrene, fluorostyrene, hydroxystyrene, divinylbenzene, etc. Consisting of polyhydric alcohol and two or more acrylic acids such as vinyl monomer, diethylene glycol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, trimethylolpropane diacrylate, trimethylolpropane triacrylate Ester compounds and the like. These may be used alone or in combination of two or more.

  Examples of other resins and rubbers preferably used include, for example, polyethylene; polyα-olefins such as polybutene-1, polyisobutene, polypentene-1, polymethylpentene-1, ethylene / butene-1 copolymer, Ethylene or α-olefin / α-olefin copolymer such as ethylene / hexene-1 copolymer, ethylene / octene-1 copolymer; ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, ethylene / Methacrylic acid copolymers, ethylene / ethyl acrylate copolymers, ethylene / butyl acrylate copolymers, ethylene / vinyl monomer copolymers such as ethylene / methyl methacrylate copolymers; polybutadiene, polyisoprene, etc. Polydiene copolymer; styrene / butadiene / styrene bromide Copolymer, styrene / ethylene-butadiene / styrene copolymer, styrene / isoprene / styrene copolymer, styrene / ethylene-propylene / styrene copolymer, styrene / isobutylene / styrene copolymer, styrene / isobutylene-butadiene / Styrene copolymer; Vinyl monomer such as acrylonitrile / butadiene / styrene graft copolymer, methyl methacrylate / butadiene / styrene graft copolymer / diene monomer / vinyl monomer graft copolymer; poly Vinyl polymers such as vinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyvinyl acetate, ethyl polyacrylate, butyl polyacrylate, polymethyl methacrylate, and polystyrene; vinyl chloride / acrylonitrile copolymer, vinyl chloride / vinyl acetate co Heavy Body, acrylonitrile / styrene copolymers, such as vinyl copolymers such as methyl methacrylate / styrene copolymer.

  Next, the polymer antistatic agent (b) used in the present invention will be described in detail.

  The polymer antistatic agent (b) used in the present invention is a component that is dispersed in the polypropylene resin (a) and imparts antistatic performance to the foamed sheet of the present invention. Moreover, since the polymer type antistatic agent (b) has a high molecular weight, it has an effect that the antistatic effect is not lowered even if the foamed sheet surface is washed with water.

  Here, “polymer type” means that the component exhibiting antistatic performance itself has a high molecular weight, and a low molecular weight surfactant (nonionic, anionic, cationic), these It does not mean that the surfactant is masterbatched with a high molecular weight matrix resin. When using a substance containing a surfactant, the problems of the present invention, such as stickiness of the surface of the foamed sheet, contamination of the package, deterioration of the antistatic effect due to washing with water, are not solved. It is impossible to obtain a foam sheet having a high closed cell ratio.

  Examples of the polymer antistatic agent (b) used in the present invention include polyethers such as polyethylene oxide and polypropylene oxide, polyether esters, polyether ester amides, ionomers such as ethylene-methacrylic acid copolymers, and polyolefins. -Polyether copolymers and the like.

  Among these, the polyolefin-polyether copolymer is preferable from the viewpoint that the dispersibility in the polypropylene resin (a) is good and the antistatic performance can be effectively exhibited even with a small addition amount. . Furthermore, a block copolymer mainly composed of a polyolefin block and a polyether block is more preferable because the above-described effect is particularly high.

  Here, the “main component” means that the block copolymer composed of the polyolefin block and the polyether block is 50% by weight or more when the total amount of the components constituting the copolymer is 100% by weight. And preferably 70% by weight or more. The ratio of polyolefin block / polyether block is preferably in the range of 3/1 to 1/3 in weight ratio.

  As a monomer which comprises the said polyolefin block, 1 type, or 2 or more types chosen from ethylene, propylene, and 1-butene are mention | raise | lifted as a preferable specific example. Moreover, as a monomer which comprises the said polyether block, 1 type, or 2 or more types chosen from ethylene oxide and a propylene oxide are mention | raise | lifted as a preferable specific example.

  The polymer type antistatic agent (b) used in the present invention has a melt flow rate (MFR) of 5.0 to 50 g measured under the condition of 2.16 kg load at 190 ° C. according to the measurement method of JIS K7210. It is preferably in the range of / 10 minutes, more preferably in the range of 10-30 g / 10 minutes. When the MFR of the polymeric antistatic agent (b) is less than 5.0 g / 10 min, the antistatic performance tends to be insufficient, and the polypropylene resin (a) and the polymeric antistatic agent are uniform. And the closed cell ratio of the resulting polypropylene resin foam sheet tends to decrease. Moreover, when the MFR exceeds 50 g / 10 min, the closed cell ratio of the foamed sheet tends to decrease.

  Specific examples of the polymer type antistatic agent (b) preferably used as described above include Pelestat 300 and Pelestat 230 manufactured by Sanyo Chemical Industries, Ltd.

  The amount of the polymeric antistatic agent (b) used in the present invention is preferably more than 2 parts by weight and 25 parts by weight or less, more than 8 parts by weight, 20 parts by weight with respect to 100 parts by weight of the polypropylene resin (a). The following is more preferable. When the amount of the polymeric antistatic agent (b) used is less than 2 parts by weight, the antistatic performance tends to be insufficient, and when it exceeds 25 parts by weight, the closed cell ratio of the obtained polypropylene resin foam sheet is lowered. It tends to be easy to do, and it tends to be disadvantageous in terms of cost.

In the present invention, by using the polymer type antistatic agent (b), the surface resistivity of the polypropylene resin foam sheet of the present invention is 1.0 × 10 ⁹ or more and less than 1.0 × 10 ¹³ Ω, especially A preferable range is 1.0 × 10 ¹⁰ or more and less than 1.0 × 10 ¹² Ω. In order to make the surface resistivity less than 1.0 × 10 ⁹ , it is necessary to increase the addition amount of the high molecular weight type antistatic agent (b), which tends to impair economic efficiency. On the other hand, at 1.0 × 10 ¹³ or more, there is a tendency that sufficient antistatic effect is not exhibited.

  The polypropylene resin foam sheet of the present invention is obtained by using a resin composition comprising 100 parts by weight of a polypropylene resin (a) and a high molecular weight antistatic agent (b) in an amount of more than 2 parts by weight and not more than 25 parts by weight. It can be obtained by using a known extrusion foaming method using

  As an extrusion foaming method used for producing the polypropylene resin foam sheet of the present invention, for example, the resin composition is melted in an extruder at 130 to 300 ° C., and then a so-called physical foaming agent is injected, kneaded and cooled. Then, a method of obtaining a foamed sheet by extruding from a die under atmospheric pressure is preferably used.

  Examples of the physical foaming agent used in this case include aliphatic hydrocarbons such as propane, butane, pentane and hexane, alicyclic hydrocarbons such as cyclopentane and cyclohexane, chlorodifluoromethane, difluoromethane, trifluoromethane, and trichlorofluoro. Methane, dichlorodifluoromethane, chloromethane, dichloromethane, chloroethane, dichlorotrifluoroethane, dichlorofluoroethane, chlorodifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane, trifluoroethane, trichlorotrifluoroethane, dichloro Inorganic such as halogenated hydrocarbons such as tetrafluoroethane, chloropentafluoroethane, and perfluorocyclobutane, carbon dioxide, nitrogen, and water Vinegar one or two or more, and the like. Of these, aliphatic hydrocarbons such as propane, butane, and pentane and carbon dioxide are preferable because they are inexpensive and have high solubility in polypropylene resins.

  The physical foaming agent may be used in an amount of 0.5 to 5 parts by weight with respect to 100 parts by weight of the polypropylene resin (a). It is in.

  As another extrusion foaming method used for producing the polypropylene resin foam sheet of the present invention, a foam nucleating agent may be added to the base resin for the purpose of adjusting the cell diameter. Specific examples of the foam nucleating agent preferably used include a mixture of sodium bicarbonate and an organic acid such as citric acid or a masterbatch thereof, talc, calcium carbonate or a masterbatch thereof.

  The amount of the foam nucleating agent used may be adjusted so as to obtain a necessary cell diameter within a range not impairing the effects of the present invention, but is usually 0.1 to 5 weights with respect to 100 parts by weight of the base resin. Within the scope of the part.

  As another example of the extrusion foaming method used in the production of the polypropylene resin foam sheet of the present invention, the resin composition and the chemical foaming agent in the form of powder or masterbatch are melt-kneaded in an extruder. A method of obtaining a foamed sheet by extruding from a die after cooling is also preferably used.

  At this time, examples of the chemical foaming agent include a mixture of sodium bicarbonate and an organic acid such as citric acid, an azo foaming agent such as azodicarbonamide and barium azodicarboxylate, N, N′-dinitrosopentamethylenetetramine, Nitroso foaming agents such as N′-dimethyl-N, N′-dinitrosotephthalamide, sulfohydrazide foaming agents such as p, p′-oxybisbenzenesulfonyl hydrazide, p-toluenesulfonyl semicarbazide, trihydrazinotriazine, etc. Can be given.

  The amount of the powder or masterbatch chemical foaming agent used to obtain the foamed sheet by the above method may be adjusted according to the target density of the foamed sheet. a) It exists in the range of 0.5-200 weight part with respect to 100 weight part.

  Further, in obtaining the foamed sheet of the present invention, an antioxidant, a metal deactivator, a phosphorus processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, a metal, depending on the purpose, in advance for the resin composition. You may add stabilizers, such as soap, or additives, such as a lubricant, a plasticizer, a filler, a reinforcing material, a pigment, dye, a flame retardant, and an antishrink agent, in the range which does not impair the effect of this invention.

  The density of the polypropylene resin foam sheet of the present invention is preferably 0.07 to 0.6 g / ml, more preferably 0.09 to 0.45 g / ml, and even more preferably 0.10 to 0.30 g / ml. When the density of the polypropylene resin foamed sheet is less than 0.07 g / ml, the rigidity for use in applications such as buffer packaging materials intended by the present invention tends to be insufficient. When the density exceeds 0.6 g / ml, there is a tendency that the buffering properties for use in applications such as the buffer packaging material intended by the present invention are insufficient.

As described above, by setting η ₀ and η ^* within the range of the present invention, even if an amount of a polymer antistatic agent necessary for exhibiting sufficient antistatic performance is added, a density of 0.07 to A polypropylene resin foam sheet having a high closed cell ratio of 0.6 g / ml can be easily obtained.

  In the present invention, in order to set the density of the polypropylene resin foam sheet within the above range, for example, a method of appropriately adjusting the amount of the foaming agent used can be mentioned. In this case, if the resin composition of the present invention is used, the density of the density associated with the decrease in closed cell ratio can be adjusted by adjusting the degree of cooling (resin temperature immediately before extrusion) by adjusting the temperature control of the extruder. It is possible to prevent the increase and easily obtain a foamed sheet having the density. The specific amount of the foaming agent is in the above-mentioned range and varies depending on the foaming agent used. For example, when butane is used as the foaming agent, in order to obtain a foamed sheet having a density of about 0.6 g / ml, polypropylene is used. It is set as the range of 0.5-0.8 weight part with respect to 100 weight part of system resin (a). Similarly, in order to obtain a foamed sheet having a density of about 0.07 g / ml, the amount is in the range of 3.4 to 4.0 parts by weight with respect to 100 parts by weight of the raw resin composition. The resin temperature at this time is preferably cooled to such an extent that crystallized resin is not generated on the surface of the foam sheet discharged from the die due to excessive cooling, and the range is approximately 160 ± 4 ° C.

  The closed cell ratio of the polypropylene resin foam sheet of the present invention is preferably 60% or more, and more preferably 70% or more. When the closed cell ratio of the polypropylene resin foamed sheet is less than 60%, the rigidity for use in applications such as buffer packaging materials intended by the present invention tends to be insufficient. Further, when the foamed sheet is molded and used, drawdown (a phenomenon in which the foamed sheet hangs down) at the time of heating increases, and there is a tendency that problems such as local thinning of the molded product tend to occur.

  In the polypropylene resin foam sheet of the present invention, the average cell diameter in the sheet thickness direction is preferably from 0.05 mm to less than 0.4 mm, more preferably from 0.08 mm to less than 0.3 mm, and from 0.1 mm to 0.2 mm. Less than is more preferable. When the average cell diameter in the sheet thickness direction of the polypropylene-based resin foam sheet is less than 0.05 mm, the rigidity for use in applications such as buffer packaging materials intended by the present invention tends to be insufficient. On the other hand, when the thickness exceeds 0.5 mm, the appearance of the foamed sheet is deteriorated, and when thermoforming is performed, the closed cell ratio is liable to decrease, and the rigidity tends to decrease.

  In the present invention, in order to set the average cell diameter in the sheet thickness direction within the above range, for example, by cooling the die for extrusion foaming, or by reducing the opening of the die lip, the resin pressure in the die The method of adjusting is mentioned. At this time, generally, the average cell diameter tends to be reduced by increasing the resin pressure. Moreover, it can also adjust by adding the said foaming nucleating agent, and an average cell diameter can be made small by increasing the addition amount of a foaming nucleating agent.

  Although there is no restriction | limiting in particular in the shape of the polypropylene resin foam sheet of this invention, Usually, it is set as the sheet form which has thickness of 0.5 mm or more and less than 8 mm, especially 1.0 mm or more and less than 6 mm. When the thickness of the polypropylene resin foam sheet is less than 0.5 mm, there is a tendency that rigidity for use in applications such as a buffer packaging material intended by the present invention is insufficient.

  The width of the polypropylene resin foam sheet of the present invention is preferably from 500 mm to 1300 mm, more preferably from 600 mm to 1200 mm. By making the width | variety of a foam sheet into this range, the application to various buffer packaging materials becomes easy.

The basis weight (weight per unit area) of the polypropylene resin foam sheet of the present invention may be appropriately changed according to the intended use, but is usually in the range of 180 to 900 g / m ² . The basis weight can be easily adjusted by changing the take-up speed of the extruded foam sheet.

  The foamed sheet according to the present invention can be formed by a known thermoforming method.

  Examples of thermoforming methods include plug molding, matched mold molding, straight molding, drape molding, plug assist molding, plug assist / reverse draw molding, air slip molding, snapback molding, reverse draw molding, free drawing molding, plug・ Methods such as AND ridge molding and ridge molding can be mentioned.

  The molded body of the present invention can be obtained by molding the foamed sheet of the present invention by the thermoforming method described above. The molded body of the present invention can be formed into a tray, a bowl, or other shapes that are not limited, and can be preferably used for food containers, buffer packaging materials, and the like.

  EXAMPLES Next, although this invention is demonstrated in detail based on an Example, this invention is not restrict | limited to this Example.

  Below, the evaluation method of the laminated foam sheet and molded object which were used for the Example and the comparative example is shown.

[Density measurement of foam sheet]
It calculated from the weight and the volume calculated | required with the submerged method with respect to the obtained foam sheet.

[Measurement of closed cell ratio of foam sheet]
The obtained foamed sheet was measured according to ASTM D-2856 using a multi-pynometer (manufactured by Yuasa Ionics).

[Average cell diameter in sheet thickness direction]
The number of cells crossed by a straight line drawn in the thickness direction was measured at 10 points on the cut surface obtained by cutting the obtained foamed sheet perpendicular to the take-up direction, and the average number of cells in the thickness direction was calculated. On the other hand, the thickness at the position was measured with calipers, and the thickness was calculated as an average value.
From the obtained thickness (mm) and the average number of cells (cells / thickness), the average cell diameter (mm) was calculated according to the formula (5).

[Surface resistivity]
The obtained foamed sheet was allowed to stand in an atmosphere of 20 ° C. and 60% humidity for 24 hours, and then measured according to JIS K6911 using a foamed sheet cut into 10 cm × 10 cm × thickness as a sample.
For the measurement, R8340 type manufactured by Advantest Corporation was used. The applied voltage was 500 V, the applied time was 1 minute, measurements were performed on five samples cut out from different locations, and the obtained values were averaged to calculate the surface resistivity (Ω) of the foam sheet.
The obtained surface resistivity was evaluated according to the following criteria.
○: Surface resistivity is less than 1 × 10 ¹² (Ω) Δ: Surface resistivity is 1 × 10 ¹² or more and less than 1 × 10 ¹³ (Ω) ×: Surface resistivity is 1 × 10 ¹³ (Ω) or more.

[Thermoformability evaluation]
The obtained foamed sheet was equipped with a far-infrared ceramic heater of 9 in the width direction and 9 in the flow direction attached to a m-width continuous vacuum forming machine (Asano Laboratories, FLC415 type). Using a zone-type heating furnace, a continuous foamed sheet was clamped with a feed chain, and heated while feeding in the direction of the molding position with a heating time of 20 seconds. At the same time, when the upper and lower surface temperatures of the foam sheet being heated were measured using a non-contact type radiation thermometer (pyrometer) provided at the center of the final zone of the heating furnace of the molding machine, the foam sheet surface temperature was 154. ° C.
Further, the foam sheet heated under the above-described conditions is a tray mold having eight rectangular storage sections in the vertical direction and 18 rectangular sections in the width direction (storage section size: length 100 mm, width 50 mm, height 20 mm, mold A molded article for evaluation was obtained by thermoforming according to a matched mold double-sided vacuum forming method using a mold clearance of 2.2 mm.
The obtained molded product was evaluated according to the following criteria.
○: Wrinkles and partially thinned parts are not observed in all of the molded products obtained in one shot.
X: Wrinkles or partially thinned parts are seen in part or all of the molded product obtained in one shot.

  Resins used in Examples and Comparative Examples are as follows.

(Production Example 1)
Raw material polypropylene (manufactured by Prime Polymer, F102W, MFR at 230 ° C. = 2 g / 10 min) 100 parts by weight and radical initiator t-butyl peroxy-isopropyl monocarbonate (Nippon Yushi Co., Ltd. perbutyl I) 0.35 A mixture obtained by stirring and mixing parts by weight with a ribbon blender is supplied to a twin-screw extruder (manufactured by Nippon Steel Works, Ltd., TEX44XCT-38) using a measuring feeder, and from the middle of the extruder using a liquid pump. Isoprene is supplied at a ratio of 0.5 parts by weight with respect to 100 parts by weight of the raw material polypropylene (blending ratio of radical polymerizable monomer to radical polymerization initiator B / A = 1.4), and the biaxial extrusion (Resin 1) pellets were obtained by melt-kneading in a machine.
The biaxial extruder was of the same direction biaxial type, the screw diameter was 44 mmφ, and the maximum screw effective length (L / D) was 38. The set temperature of the cylinder part of this twin-screw extruder was 180 ° C. until isoprene monomer injection, 200 ° C. after isoprene injection, and the screw rotation speed was set to 120 rpm.

(Production Examples 2 to 7)
As shown in Table 1, except that the type of raw material polypropylene, the blending amount of radical initiator, the blending amount of isoprene (blending ratio B / A of radical polymerizable monomer to radical polymerization initiator) were changed, respectively. By the same operation as (Resin 1), pellets of (Resin 2) to (Resin 7) were obtained.

Table 1 shows the zero shear viscosity η ₀ at 210 ° C. of the resins (resin 1) to (resin 7), which are polypropylene resins used as (resin a) in Examples and Comparative Examples, and the frequency 100 ( The complex viscosity η ^* at (/ sec) is shown.

(Resin 8)
A mixture composition comprising 70 parts by weight of (Resin 1) and 30 parts by weight of a homopolymer made of prime polymer (F113G, MFR at 230 ° C. = 3 g / 10 minutes) was used. Here, η _{0 of} the composition calculated from the formula (3) is 2.43 × 10 ⁵ Pa · sec, and the complex viscosity η ^* at a frequency of 100 (/ sec) calculated from the formula (4) is 580 Pa · sec. there were.

(Resin 9)
Sun Allomer homopolypropylene, PF-814 (MFR at 2.16 kg load at 230 ° C. = 3 g / 10 min, η _{0 at} 210 ° C. = 0.14 × 10 ⁵ Pa · sec, frequency 100 at 210 ° C. (/ sec) Complex viscosity η ^* = 290 Pa · sec)
(Resin 10)
Sun Allomer polypropylene-polyethylene block copolymer, SD-632 (230 ° C., MFR at 2.16 kg = 3 g / 10 min, η _{0 at} 210 ° C. = 0.13 × 10 ⁵ Pa · sec, frequency at 210 ° C. Complex viscosity at 100 (/ sec) η ^* = 280 Pa · sec)

The antistatic agents used in Examples and Comparative Examples are as follows.
Antistatic agent T1: High molecular weight type antistatic agent, manufactured by Sanyo Chemical Industries, Pelestat 300 (MFR at 2.16 kg load at 190 ° C. = 30 g / 10 min)
Antistatic agent T1: High molecular weight type antistatic agent, manufactured by Sanyo Chemical Industries, Pelestat 230 (MFR at 190 ° C. under 2.16 kg load = 10 g / 10 min)
Antistatic agent T1: Nonionic surfactant type antistatic agent, manufactured by Kao Corporation, Electro Stripper TS-3B

(Example 1)
As a polypropylene resin (a), 100 parts by weight of (Resin 1), and as a high molecular weight type antistatic agent (b), manufactured by Sanyo Chemical Industries, Pelestat 300 (MFR at 190 ° C. under a 2.16 kg load = 30 g) / 10 minutes) To a resin composition consisting of 10 parts by weight, 1.0 part by weight of a master batch of sodium bicarbonate-organic acid chemical foaming agent (manufactured by Dainichi Seika Co., Ltd., PO510K) was added and mixed with a ribbon blender.
The above blend was supplied to a 90-125 mmφ tandem extruder and melted in a first stage extruder (90 mmφ) set at 200 ° C., and then isobutane as a foaming agent (resin 1) per 100 parts by weight 2.0 parts by weight is injected and mixed, cooled in a second-stage extruder (125 mmφ) set at 160 ° C. (measured by a temperature sensor installed in the resin inflow part of the die), and atmospheric pressure from a circular die (caliber 127 mmφ) The product was discharged downward, drawn and cooled while being molded in a cooling cylinder having an outer diameter of 335 mm and a body length of 800 mm to obtain a cylindrical foam, which was cut open with a cutter to obtain a foam sheet having a width of 1035 mm.
Using the obtained foamed sheet, the thickness, density, closed cell ratio, average cell diameter and surface resistivity in the sheet thickness direction were measured, and further, heat moldability evaluation was performed. The results are shown in Table 2.

(Examples 2-13, Comparative Examples 1-7)
As shown in Table 2, foaming was performed in the same manner as in Example 1 except that the type and blending amount of the polypropylene resin (a), the high molecular weight type antistatic agent (b), and the amount of foaming agent used were changed. A sheet was obtained.
Using the obtained foamed sheet, the thickness, density, closed cell ratio, average cell diameter and surface resistivity in the sheet thickness direction were measured, and further, heat moldability evaluation was performed. The results are shown in Table 2 or Table 3.

(Comparative Example 8)
Instead of the high molecular weight type antistatic agent (b), as a low molecular weight type antistatic agent, 1.0 part by weight of a nonionic surfactant (manufactured by Kao Corporation, Electro Stripper TS-3B) was used. A foamed sheet was obtained in the same manner as in Example 1.
Using the obtained foamed sheet, the thickness, density, closed cell ratio, average cell diameter and surface resistivity in the sheet thickness direction were measured, and further, heat moldability evaluation was performed. The results are shown in Table 3.

As is apparent from Tables 2 and 3, the polypropylene resin foam sheet of the present invention comprises a polypropylene resin (a) exhibiting specific viscoelastic properties (η ₀ and η ^* ) and a high molecular weight antistatic agent (b ), It is possible to have both a sufficient antistatic effect and a high closed cell ratio even in a density range of 0.07 to 0.6 g / ml, which is suitable as a buffer packaging material. Further, the cell diameter is not roughened with the addition of the high molecular weight type antistatic agent (b), and fine cells can be provided.

Furthermore, the foamed sheet of the present invention can be easily formed by thermoforming into the molded product of the present invention without appearance defects such as wrinkles.

Claims (6)

With respect to 100 parts by weight of the polypropylene resin (a) in which the zero shear viscosity η ₀ at 210 ° C. and the complex viscosity η ^* at a frequency of 100 (/ sec) at 210 ° C. satisfy the following expressions (1) and (2): And a polypropylene-based resin foam sheet obtained by extrusion foaming a resin composition containing more than 2 parts by weight and less than 25 parts by weight of the polymer antistatic agent (b), and having a density of 0.07-0. A polypropylene resin foam sheet having 6 g / ml and a closed cell ratio of 60% or more.

  The polypropylene resin foam sheet according to claim 1, wherein the resin composition contains a polymer-type antistatic agent (b) in an amount of more than 8 parts by weight and 25 parts by weight or less.   The polypropylene resin foam sheet according to claim 1 or 2, wherein the closed cell ratio is 70% or more.   The polypropylene resin foam sheet according to any one of claims 1 to 3, wherein an average cell diameter in a sheet thickness direction is 0.05 mm or more and less than 0.4 mm.   The polypropylene resin foam sheet according to any one of claims 1 to 3, wherein an average cell diameter in the sheet thickness direction is 0.1 mm or more and less than 0.2 mm.   The molded object obtained by thermoforming the polypropylene-type resin foam sheet in any one of Claims 1-4.