JPH0246387B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a so-called tarpaulin sheet made of a synthetic fiber woven fabric as a base material and a soft synthetic resin material laminated on both sides by calendering or laminating. Tarpaulin sheets have been used as industrial intermediate materials in a wide range of applications such as civil engineering, logistics, fisheries, mining, and construction. Along with the expansion of such uses, the functions of tarpaulin sheets required by the market are diversifying, and one of these functions is antistatic function, which has become increasingly important in recent years. For example, in flexible containers used for transporting and storing powder and granular materials, due to the properties of the powder and granular materials, high voltage is generated due to frictional electrification during loading and unloading, and there is a risk of discharge. Furthermore, in applications such as tarpaulin flexible ducts (generally referred to as wind pipes) used for ventilation and ventilation in mines, prevention of static electricity on tarpaulins is essential. The antistatic method for general tarpaulins is usually applied to the soft synthetic resin that is the coating material, and is highly effective. To prevent static electricity on such synthetic resins, internal antistatic agents (kneading agents) and external antistatic agents (coating agents, antistatic paints) are used. It has no long-lasting effect and is not suitable for tarpaulins.
In addition, antistatic agents for internal use can be roughly divided into two methods: a method in which conductive fine powder such as carbon black or metal is kneaded into a synthetic resin, and a method in which a surfactant is kneaded. However, when used for tarpaulins, there are various obstacles to using these antistatic agents. For example, a method of kneading conductive fine powder into synthetic resin cannot be used because it generates sparks during high-frequency welding, which is widely used as a secondary processing method for tarpaulin sheets. Additionally, in order to achieve the required conductivity, a large amount of fine powder (10 to 20 parts) must be kneaded in, which impairs the tarpaulin's original function and makes it less flexible. It is not possible to color freely. In addition, when using a surfactant, the surfactant dissipates during long-term use of the tarpaulin, and the antistatic effect cannot be expected to last long. There are problems such as sometimes inhibiting welding and lacking the necessary welding strength. Tarpaulins have the above-mentioned problems in preventing static electricity, and for example, when used as flexible containers, the only tarpaulins currently on the market are synthetic rubber tarpaulins mixed with carbon black. Such synthetic rubber tarpaulins are made of polyvinyl chloride (hereinafter sometimes simply referred to as PVC),
Ethylene-vinyl acetate copolymer (hereinafter simply EVA)
It is sometimes called. ) tarpaulin, high-frequency welding as a secondary processing method is not possible, so rubber glue is used for bonding. Therefore, the reality is that there is currently no suitable method for preventing static electricity on PVC and EVA tarpaulins. The present invention has been made to solve the above problems, and contains an antistatic agent that is a fatty acid monoester of glycerin, and the fatty acid is a mixture of palmitic acid and stearic acid, from 0.1 to 3% by weight. This is a tarpaulin whose coating material is made of synthetic resin. The tarpaulin of the present invention has a long-lasting antistatic ability and can be processed by high frequency welding.
This is an extremely useful tarpaulin. The synthetic resins used in the tarpaulin of the present invention include ethylene/vinyl acetate copolymer, polyvinyl chloride, polyurethane, ethylene, vinyl acetate, vinyl chloride copolymer, chlorinated polyethylene, ethylene/ethyl acrylate copolymer, etc. Among them, ethylene, vinyl acetate copolymers,
Polyvinyl chloride is preferred. In particular, as an ethylene/vinyl acetate copolymer, the vinyl acetate content is 5 to 30% by weight, preferably 15 to 25% by weight.
% by weight, MI in the range from 0.5 to 5, preferably from 0.5 to 2, are preferably used. Additionally, polyvinyl chloride generally has a polymerization degree of 1000~
1300 is preferred and is used in combination with a plasticizer such as dioctyl phthalate (DOP) or dibutyl phthalate (DBP). The amount of plasticizer added is 40 to 60 parts by weight per 100 parts by weight of the polyvinyl chloride compound. In order to use these synthetic resins for the tarpaulin of the present invention, various additives can generally be mixed therein. These compounding agents include stabilizers, lubricants, pigments, etc., and these are usually 0 to 5% of the synthetic resin.
It is used in a range of 0 to 3% by weight, preferably 0 to 3% by weight. The antistatic agent added to the synthetic resin, which is an essential component in the present invention, is a fatty acid monoester of glycerin, where the fatty acid is a mixture of palmitic acid and stearic acid, and other antistatic agents. With antistatic agents, the antistatic ability or durability is low, or high frequency welding cannot be performed. In addition, even when the fatty acid is palmitic acid alone, its persistence is excellent, but the initial antistatic ability is insufficient, and even when stearic acid is used alone, both the initial antistatic ability and its sustainability are poor. There is no other choice. The tarpaulin of the present invention uses a synthetic resin blended with the above-mentioned antistatic agent, and there are generally dry blending methods, masterbatch methods, etc., among which the masterbatch method is preferred. A concrete example of this blending method is as follows. In advance, the above antistatic agent is blended in an amount that is 10 to 20 times the concentration required for the synthetic resin using a blender or super mixer, and this is granulated using an extruder or mixing roll to form a master batch. Create. Next, this masterbatch is blended with 10 to 20 times more synthetic resin to achieve the concentration set during molding, and is plasticized to form a coating material. This master batch method is the most suitable method for uniformly blending a low concentration additive into a synthetic resin as in the present invention. In the synthetic resin of the tarpaulin of the present invention, the content of antistatic agent is 0.1 to 3% by weight, preferably 0.2% by weight.
~2.0% by weight, most preferably 0.5-1.5% by weight. If the content of the above-mentioned antistatic agent is too small, the antistatic effect will be insufficient, and if the content is too high, it will precipitate out to the surface within about one day after forming the sheet, and the antistatic ability will be lower than that. Doesn't improve. This is because although the fatty acid monoester of glycerin in the present invention has high compatibility with the polymer, if it is mixed in at a concentration higher than the dissolved concentration with the polymer, it will precipitate out on the surface. Therefore, since the antistatic effect is also the same above a certain concentration, there is an optimum mixing amount. Specifically, it is 1 to 3% by weight, preferably 1 to 2% by weight for EVA resin, and 0.1 to 3.0% by weight, preferably 0.2 to 2% by weight for PVC resin. In order for a surfactant to function effectively as an antistatic agent, it is said that a uniform molecular layer is formed on the surface of a charged body, and this molecular layer provides conductivity through moisture adsorption or the like. However, according to this idea, an extremely thin layer of surfactant is formed on the surface of the tarpaulin, which changes the surface properties of the tarpaulin and interferes with high-frequency welding processing.Also, the surface layer is dissipated during cleaning and other processes, preventing static electricity. It is expected that the effectiveness will decrease. The inventors conducted various experiments and found that in order for a surfactant to exhibit an antistatic effect, it is not necessary to form a uniform molecular layer on the surface, but rather a microscopic dispersion on the order of molecules occurs near the surface layer. It was estimated that a sufficient antistatic effect could be obtained if the
Therefore, it is based on the idea that if a surfactant that is highly compatible with the polymer and has a high antistatic effect can be selected, it is possible to prevent the tarpaulin from becoming statically charged. From this point of view, as a result of experiments and evaluations of various antistatic agents, it was found that a fatty acid monoester of glycerin, in which the fatty acid is a mixture of palmitic acid and stearic acid, is most suitable. Ta. Of course, compatibility must be considered in relation to the polymer and the results are particularly good for PVC and EVA resins for tarpaulin applications. Fortunately, both are soft materials, and the fatty acid monoester of glycerin in the present invention is thought to be dissolved in the plasticizer portion in PVC and the vinyl acetate group in EVA. In addition, the −OCOR group in the fatty acid monoester of glycerin maintains compatibility with the polymer, and the OH
It is thought that the material exhibits electrical conductivity in some parts. Generally speaking, the antistatic properties of tarpaulin are as follows: Volume resistivity is generally 10 ¹⁰ Ω cm or less, commercially available PVC tarpaulin (contains 50 parts of plasticizer DOP, polyester woven fabric) is 1.0 x 11 ¹¹ Ω cm or more, EVA tarpaulin ( (20% vinyl acetate content, polyester woven fabric used)
It is 1.0×10 ¹² Ωcm or more. The tarpaulin of the present invention is manufactured by applying a synthetic resin containing the above-mentioned antistatic agent to a base fabric, and the base fabric used in the present invention includes synthetic fibers such as polyester, polyamide, polyolefin, and polyacrylic. There are also fabrics in which filaments or staples of various natural or semi-synthetic fibers are woven into plain weave, twill weave, satin weave, etc. Among these base fabrics, plain weave of polyester or polyamide is preferred. These base fabrics have a thickness of 0.2~
2 mm and a width of about 0.5 to 3 m is generally used. Methods for coating these base fabrics include calendering, extrusion lamination, dry lamination, and impregnation, among which calendering is preferred. The tarpaulin of the present invention thus obtained can be used in container bags, conveyor belts, open pile sheets, etc.
It can be used as a material for curing sheets, car tops, water tanks, etc. In order to be used for these purposes, they are cut and welded, and the cutting is done with a cutter or scissors, and the welding is usually done by high frequency welding. The high frequency welding method uses a high frequency welding machine within the frequency range of 10 to 100MHz, usually 27.17MHz.
Alternatively, it is welded by processing at 40.68MHz for a welding time of 10 to 60 seconds, preferably 10 to 30 seconds. Various bags and cloths obtained by processing the tarpaulin of the present invention have extremely excellent antistatic properties even when used for transporting and discharging powder particles. Next, examples are shown below. Example 1 EVA resin (EVA-1905 manufactured by Mitsui Polychemical Co., Ltd.)
MI = 2.5 vinyl acetate content 20%) 100 parts of glycerin fatty acid monoester (a mixture of 50 parts by weight of glycerin palmitate monoester and 50 parts by weight of glycerin stearate monoester), 1.5 parts of other stabilizers,
Blended with pigment, this EVA resin composition is heated and rolled to form a coating film of 0.4 mm. This is heated with a calendar roll at a temperature of 140℃ to 160℃ to form polyester plain woven fabric (16 pieces of 1000 denier manufactured by Teijin). A tarpaulin was created by laminating on both sides of 17 pieces/inch). The electrical resistance values of this tarpaulin are shown in Table-1. This tarpaulin was cut to a width of 1 m x 1 m, washed for 24 hours, and then left in the atmosphere for 24 hours as one cycle, and the electrical resistance value was measured after 10 cycles. As a result, the volume resistivity value was 5.6 × 10 ⁹ Ωcm, and the surface resistivity value was 2.6 × 10 ⁶ Ω, which was almost the same as before washing (cleaning conditions: 40°C, Neugen EA), although the resistance value showed a slight tendency to increase. −120 (1st
(manufactured by Kogyo Seiyaku Co., Ltd.) 4%). Furthermore, two tarpaulins of the present invention were stacked and high-frequency welded, and the welding processability and welding strength were compared with EVA tarpaulin. As shown in the table, there were no problems with high frequency welding. Comparative Example 1 No fatty acid monoester of glycerin was added,
EVA was created under the same conditions as Example 1.
It was compared with the electrical resistance value of tarpaulin. The results are shown in Table.

【table】

【table】

[Table] Example 2 PVC resin (TK-1000 manufactured by Shin-Etsu Chemical Co., Ltd. Polymerization degree
1050), 50 parts of plasticizer DOP, 0.5 part of fatty acid monoester of glycerin (a mixed part of 50 parts by weight of glycerin palmitate monoester and 50 parts by weight of glycerin stearate monoester), other stabilizers, and pigments, and this A PVC tarpaulin was produced by laminating the PVC resin composition on a polyester woven fabric under exactly the same conditions as in Example 1. The electrical resistance value of this tarpaulin is shown in the table. In addition, the tarpaulin of the present invention was examined for changes in resistance after washing, high-frequency workability, and welding strength in the same manner as in Heavy Example 1, but the electrical resistance value did not change at all, and the high-frequency welding workability and welding strength were investigated. There was no change in either. Comparative Example 2 No fatty acid monoester of glycerin was added,
The electrical resistance values of PVC tarpaulins made under the same conditions were compared. The results are shown in Table.

[Table] Comparative Examples 3 to 5 In place of the glycerin fatty acid monoester of the present invention, typical commercially available antistatic agents such as Chemistat 1005 (cationic type manufactured by Sanyo Chemical Co., Ltd.) and Resistut 212 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd. anionic) were used. system), TB
-128 (Matsumoto Yushi Seiyaku's alkylamine type), a tarpaulin was produced in the same manner as in Examples 1 and 2, and the electrical resistance value and high frequency processability of the tarpaulin were evaluated. The results are shown in Table.

[Table] Example 3 The electrical resistance values of the tarpaulins obtained in Example 1 when the amount of fatty acid monoester of glycerin added was varied are shown in the table.

[Table] * Glycerin fatty acid monoester precipitates from the tarpaulin surface.
Example 4 Table 1 shows the electrical resistance values of the tarpaulin when the amount of fatty acid monoester of glycerin added in Example 2 was changed.

[Table] Reference Examples 1 to 3 To 100 parts of the EVA resin of Example 1, as a fatty acid monoester of glycerin as an antistatic agent, the fatty acid is a mixture of palmitic acid and stearic acid (Reference Example 1), palmitin One part of acid alone (Reference Example 2) and one part of stearic acid alone (Reference Example 3) were each mixed, and a sheet with a thickness of 0.4 mm was created by hot pressing. The surface resistivity of each sheet obtained was measured, and the surface resistivity after washing for 100 hours under the same conditions as in Example 1 was also measured. The results are shown in Table.

【table】

Claims (1)

[Claims] 1 A fatty acid monoester of glycerin,
A tarpaulin whose coating material is a synthetic resin containing 0.1 to 3% by weight of an antistatic agent whose fatty acids are a mixture of palmitic acid and stearic acid.