JPH0576167B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention has a high amount of trapped charge,
Regarding an electret material that has stable electret performance over a long period of time and has excellent formability, and a method for producing the same, in particular, for example, when the electret material is a melt-blown nonwoven fabric, it has very good melt-blown spinnability. The present invention relates to an electret material characterized by the following features: and a method for producing the same. [Prior art] Conventionally, as a method for electrifying high molecular weight polymers, the electrostatic handbook (published by Ohmsha Showa) was used.
Published on May 30, 1956), page 155, and Japanese Patent Application Publication No. 1983
Various methods are known, such as those described in Publication No. -289177, but all of them ultimately result in
In this method, injection of electrons, movement of ions, orientation of dipoles, etc. are caused in a sheet structure made of a high molecular weight polymer, thereby polarizing the sheet and imparting an electric charge to the sheet. On the other hand, as one of the electrification techniques to obtain a particularly high electrification effect, it has been proposed to add a compound to a high molecular weight polymer to impart an electrification effect to produce an electret material. There is a method described in Japanese Patent Application Laid-Open No. 196922/1983. However, in the method described in the above-mentioned publication in which polypropylene is blended with a resin acid metal salt and subjected to corona treatment, although the amount of trapped charge increases to some extent and the electrification effect is improved,
That alone was not at a level that could be used as a sufficient electret material. In addition, when providing an electret material made of melt-blown nonwoven fabric, due to its spinning principle, the melt viscosity at the nozzle must be approximately 30 poise to 150 poise, so it is necessary to use a low-viscosity polymer or spin at high temperature. It was necessary. [Problems to be Solved by the Invention] An object of the present invention is to provide an electret material that eliminates the drawbacks of such conventional products and a method for producing the same. The object of the present invention is to provide an electret material that has stable electret performance over a long period of time, excellent moldability, and particularly facilitates melt blow spinnability, and a method for producing the same. [Means for Solving the Problems] The electret material of the present invention that achieves the above-mentioned object is made of a polypropylene molded product containing 5 to 70 parts by weight of petroleum resin that does not contain polar groups to 100 parts by weight of polypropylene. It is an electret material. In addition, the method for producing an electret material of the present invention includes forming a polypropylene molded article by blending 5 to 70 parts by weight of a petroleum resin that does not contain polar groups to 100 parts by weight of polypropylene, and then subjecting the molded article to electret treatment. This is a method for producing an electret material characterized by the following. [Function] The present invention will be explained in detail below. As a method for electrifying a high molecular weight polymer, the present inventors continued various studies regarding the high molecular weight polymer composition, and discovered that 5 to 70 parts by weight of petroleum resin containing no polar groups was added to 100 parts by weight of polypropylene. It has been found that by forming a polypropylene molded article using a partially blended polypropylene resin and then subjecting the molded article to an electret treatment, an electret material with good moldability and a high level of quality can be obtained. The polypropylene used in the present invention may be of any type, but preferably has a sharp molecular weight distribution expressed by the ratio of Mw (weight average molecular weight)/Mn (number average molecular weight) in order to enhance the electrification effect. Preferably, specifically,
It is preferable to use one with a Mw/Mn ratio of 5.5 or less.
More preferably, the number is 4 or less. Methods for sharpening the molecular weight distribution include (1) mixing a radical generator with polypropylene for degradation, (2) thermal degradation, (3) kneading and degradation, ( 4) There are methods to degrade the material by irradiating it with radiation. According to the findings of the present inventors, the most effective method is to mix polypropylene powder with a radical generator, heat stabilizer, etc. This is a method of degrading in an extruder, but it is not particularly limited to this method. In the case of the above method, various peroxides, diazo compounds, tin compounds, etc. can be used as the radical generator, and the mixing ratio depends on the type,
Although it should be changed as appropriate depending on the degradation temperature, degradation time, and other compounding agents mixed, it is generally good to use 0.0005 parts by weight to 0.5 parts by weight based on polypropylene. . The petroleum resin that does not contain polar groups and is used as part of the substances constituting the material of the present invention refers to hydroxyl groups,
carboxyl group, halogen group, sulfone group, etc.
Alternatively, it refers to petroleum resins that do not have polar groups and are made from modified products of these, i.e., cyclopentadiene-based resins made directly from petroleum-based unsaturated hydrocarbons, or resins whose main raw materials are higher olefin-based hydrocarbons. be. It is preferable for the present invention to use a petroleum resin having a glass transition temperature Tg of 50° or more. Furthermore, hydrogen is added to the petroleum resin to increase the hydrogenation rate to 80% or more, preferably 95%.
In the case of the present invention, it is particularly preferable to use the above hydrogenated petroleum resin. Typical resins that can be used in the present invention include, for example, hydrogenated alicyclic petroleum resins containing the compounds shown below as main components.

According to the findings of the present inventors, it is important to blend the above-mentioned petroleum resin in the range of 5 to 70 parts by weight with respect to 100 parts by weight of polypropylene, and if it is less than 5 parts by weight, electrification may occur. The effect of improving the spinning temperature is not sufficient, and the effect of lowering the spinning temperature is small, which is not preferable. Moreover, if it exceeds 70 parts by weight, it is not preferable because the good spinnability of polypropylene is impaired and the propylene molded article tends to become brittle. In the present invention, the polypropylene resin further includes at least one stabilizer selected from among a hindered amine type, a nitrogen-containing hindered phenol type, a metal salt hindered phenol type, a phenol type, a sulfur type, and a phosphorus type stabilizer based on 100 parts by weight of the polypropylene. It is preferable to use a mixture containing 0.01 part by weight or more and 2 parts by weight or less. For example, in the case of hindered amine stabilizers, poly[{(6-
(1,1,3,3,-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl}
{(2,2,6,6,-tetramethyl-4-piperidyl)imino}hexamethylene {(2,2,6,
6-tetramethyl-4-piperidyl)imino},
Dimethyl-1-(2-hydroxyethyl) succinate
-4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate, 2-(3,5-di-t-
butyl-4-hydroxybenzyl)-2-n-butylmalonic acid bis(1,2,2,6,6-pentamethyl-4-piperidyl), etc. can be used, and nitrogen-containing hindered phenol-based ones can be used. Then, 1,3,5-tris(4-t-butyl-3
-hydroxy-2,6-dimethylbenzyl)isocyanuric acid, or 1,3,5-tris(3,
5-di-t-butyl-4-hydroxybenzyl)
Isocyanuric acid and the like can be used. In addition, the metal salt hindered phenol type includes calcium salt of 3,5-di-t-butyl-4-hydroxy-benzyl-mono-ethyl-phosphonate, 3,5-di-t-butyl-4-hydroxy-
The nickel salt of benzyl-mono-ethyl-phosphonate or the magnesium salt of the above compound can be used. In addition, phenolic ones include 1,3,5-
Trimethyl-2,5,6-tris(3,5-di-
t-Butyl-4-hydroxybenzyl)benzene, pentaerythrityl-tetrakis [3-(3,
5-di-t-butyl-4-hydroxyphenyl)
propionate], octadecyl-3-(3,5-
Di-t-butyl-4-hydroxyphenyl) propionate and the like can be used. Further, as the sulfur-based material, distearyl thiodipropionate, dilauryl thiodipropylnate, etc. can be used. According to the findings of the present inventors, the effect of electrification is further improved by blending one or more of these stabilizers into polypropylene. Furthermore, a UV absorber (for example, benzotriazole type) may be used in combination. Further, these stabilizers may be added at the stage of pelletizing polypropylene. The blending ratio of the above-mentioned stabilizer is preferably 0.02 parts by weight to 0.7 parts by weight,
More preferably, it is 0.05 part by weight to 0.5 part by weight. In the present invention, a thermoplastic resin such as a homopolymer or copolymer such as polyester, polyolefin, polycarbonate, or polystyrene may be further blended with the polypropylene resin. The blending amount is preferably about 20 parts by weight at most. It is desirable that the thermoplastic resin has good compatibility with polypropylene, and it is preferable to select a polymer whose melt viscosity during molding is close to that of polypropylene. As the amount of the compound increases, the amount of trap charge decreases,
Since this may lead to unstable molding, the amount is preferably 10 parts by weight or less, more preferably 5 parts by weight or less. The electret material of the present invention can take various forms such as a sheet, a film, a fibrous material, a pipe, and a composite sheet made of multiple fibrous materials. In the present invention, any form exhibits a high electret effect, but those made of fibrous materials, especially sheet-like materials made of ultrafine fibrous materials (for example, melt-blown nonwoven fabrics with an average fineness of 0.1 denier or less)
is a very preferable example. For example, when an electret sheet made of fibrous material is used as the overmaterial, the amount of trapped charge from the heat-stimulated depolarization current is 2.0×10 ^-10
It is desirable to use an electret material with a coulomb/cm2 ^or higher, particularly preferably 5.0×
It is said that it is preferable to use an electret material with a capacity of 10 ^-10 coulombs/cm ² or more, but for example,
As an example, average fineness 0.03 denier, basis weight 20g/
The electret material of the present ^invention made of a melt-blown non-woven fabric of 5.0 x 10 ^-10 coulombs/cm ² or higher, which is a very high level, according to the present invention. It is possible to provide materials that can achieve even higher performance than conventional products in the pharmaceutical field. [Example] The present invention will be described below according to Examples. In the following examples, the amount of trapped charge from the heat-stimulated depolarization current was measured as follows. That is, the method for measuring the amount of trapped charge from a heat-stimulated depolarization current is as shown in the schematic diagram of FIG. , 8, and connect this electrode to a high-sensitivity ammeter 9 for measurement. That is, the heating tank is heated at a constant rate, e.g.
When the temperature is raised from room temperature to near the melting point at a rate of 5°C/min, the trapped charges are depolarized and a current flows. When this current is recorded on the recorder 11 via the data processing device 10, depolarized current curves for various temperature ranges are obtained. The quotient (unit: clones/cm ² ) obtained by dividing the area of this current curve by the area of the measurement sample is called the amount of trapped charge. In this measurement, the higher the trap charge amount side is located, the more stable the electret is, and the larger the trap charge amount, the higher the electret effect. Example 1, Example 2 and Comparative Example 0.03 parts by weight of 2,6-di-t-butyl-p-cresol was blended as a base stabilizer to 100 parts by weight of polypropylene, and calcium stearate was added as a halogen scavenger. Pentaerythrityl-tetrakis [3-(3,5-
By mixing 0.1 part by weight of di-t-butyl-4-hydroxyphenyl propionate and degrading it by mixing with a radical generator, the MI was 28 and Mw/
Pellets with Mn of 5.4 were produced. There are two cases, one in which 50 parts by weight of hydrogenated alicyclic petroleum resin is uniformly blended, and the other in which 30 parts by weight is uniformly blended (the former is Example 1 and the latter is Example 2). Regarding the case where the hydrogenated alicyclic petroleum resin is not blended (comparative example), by the melt blow method,
A nonwoven fabric sheet was obtained by melt blow spinning to have a basis weight of 30 g/m ² and an average fiber diameter of approximately 0.03 denier. The spinning molding temperature at this time can be set lower than when the hydrogenated alicyclic petroleum resin is not blended, by 18°C when 50 parts by weight is blended, and by 12°C when 30 parts by weight is blended, making it stable. reduction in agent consumption;
The spinning atmosphere could be kept at a lower temperature, and spinning could be carried out favorably. This sheet was subjected to electret processing using the apparatus shown in FIG. In the figure, 1 is a needle electrode;
2 is a ground electrode, 3 is a semiconductive sheet,
4 is a nonwoven fabric sheet, and the processing conditions are a temperature of 25
℃ in an atmosphere with 65% humidity, the distance between the needle electrode 1 and the nonwoven fabric sheet 4 was 5 cm, and the applied voltage was -40 Kv.
Electret processing was performed with an application time of 10 seconds. The electret levels of three types of electret-treated nonwoven fabric sheets 4 were determined from the heat-stimulated depolarization currents, and the results are shown in Table 1.

[Table] From Table 1, compared to Comparative Example 1, Examples 1 and 2 have a very high electrification effect as measured by the amount of trapped charge, and are excellent as electret materials with very high performance. I understand that. [Effects of the Invention] As described above, the electret material and method for producing the same of the present invention provide an electret material that has a high amount of trapped charge, is stable over a long period of time, and has excellent moldability, and its production. A method is provided. Therefore, due to its electret performance,
It is suitable not only for various filter materials, but also for general filters, wiper materials, adsorption materials, mask members, dustproof clothing members, etc., and can be used for a wide range of purposes.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view illustrating an example of an electret processing method, and in particular, a method employed in the examples. FIG. 2 is a schematic diagram illustrating a method for measuring the amount of trapped charge from a thermally stimulated depolarizing current. DESCRIPTION OF SYMBOLS 1... needle-shaped electrode, 1... needle-shaped electrode, 2... earth electrode, 3... semiconductive sheet, 4... nonwoven fabric sheet, 4a... electret material, 5... temperature control device, 6... heating tank, 7... Electrode, 8... Electrode, 9... High sensitivity ammeter, 10... Data processing device, 11... Recorder.

Claims (1)

[Scope of Claims] 1. An electret material comprising a polypropylene molded article containing 5 to 70 parts by weight of a petroleum resin containing no polar groups based on 100 parts by weight of polypropylene. 2. The electret material according to claim 1, wherein the molded article is a melt-blown nonwoven fabric. 3. A polypropylene molded body is prepared using a polypropylene resin containing 5 to 70 parts by weight of a petroleum resin that does not contain polar groups based on 100 parts by weight of polypropylene, and then the polypropylene molded body is subjected to an electrification treatment. A method for producing an electret material. 4 Polypropylene as polypropylene resin
At least one or more of hindered amine, nitrogen-containing hindered phenol, metal salt hindered phenol, phenol, or sulfur stabilizers are added to 100 parts by weight from 0.01 part by weight to 2 parts by weight. 4. The method for producing an electret material according to claim 3, characterized in that a blended electret material is used. 5. The method for producing an electret material according to claim 3 or 4, wherein the molded article is a melt-blown nonwoven fabric.