JPH0566422B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Purpose of the invention [Field of industrial application] The present invention relates to a one-component conductive paint suitable for use in electromagnetic shielding materials, membrane touch switches, circuit printing, etc. It provides an excellent paint. [Prior art and its problems] Carbon-based paints are often used as conductive paints for membrane touch switches such as calculators, copy machines, televisions, and microwave ovens due to their low cost. Thermoplastic resins such as vinyl chloride-vinyl acetate copolymers or blend polymers of vinyl chloride-vinyl acetate copolymers and polyvinyl butyral or polybutene have been preferably used as binders because of their excellent flexibility and durability. However, conductive paints using the above-mentioned copolymers or blended polymers as binders do not have sufficient adhesion to flexible substrates made of polyester resins or polycarbonate resins for membrane touch switches, and their flexibility is also inadequate. As a result, membrane touch switches using this have a problem in that the coating film peels off from the substrate after repeated use over a long period of time. The present invention relates to a conductive paint that solves this problem. (B) Structure of the Invention [Means for Solving the Problem] The present invention is directed to the use of vinyl chloride monomer or a monomer mixture of vinyl chloride monomer and a monomer copolymerizable therewith in 100 parts by weight. On the other hand, in the presence of 3 to 100 parts by weight of a thermoplastic polyurethane elastomer that is soluble in the monomer or monomer mixture and has a softening point of 20 to 100°C,
This is a conductive paint made by dispersing carbon black or carbon black and graphite in a solvent solution of a thermoplastic resin obtained by polymerizing the monomer or monomer mixture. The present invention will be explained in detail below. [Thermoplastic resin] As mentioned above, the thermoplastic resin in the present invention is a vinyl chloride monomer (hereinafter abbreviated as MVC) or a monomer mixture of MVC and a monomer copolymerizable with MVC ( A thermoplastic polyurethane elastomer (hereinafter referred to as MVC-soluble TPU) that is soluble in the MVC monomer and has a softening point of 20 to 100° C. is added to 100 parts by weight (hereinafter, these are collectively referred to as MVC monomers). ) to 3
This is a polymer obtained by polymerizing MVC monomers in the coexistence of ~100 parts by weight. This thermoplastic resin has
It is presumed that a graft copolymer with MVC-soluble TPU as the backbone polymer and a polymer composed of MVC monomers as the branch polymer is included, and due to the presence of this graft copolymer, the membrane It shows good adhesion to the flexible substrate made of polyester resin or polycarbonate resin of the touch switch, and the flexibility of the thermoplastic resin is sufficient for the coating film formed from the conductive paint made of it. It is presumed that the [MVC soluble TPU] The MVC soluble TPU in the present invention refers to MVC
Under the polymerization conditions of the monomers in the system, substantially MVC
It is soluble in the system monomer and has a softening point of 100~
20°C, preferably 60-30°C. Softening point
If it exceeds 100°C, it will be difficult to dissolve in the MVC monomer, and if it is below 20°C, the resulting polymer will have poor mechanical strength and heat resistance. The softening point in the present invention refers to the softening temperature determined by the temperature increase method using a Shimadzu Koka type flow tester under the following conditions. Measurement conditions for Shimadzu Koka flow tester Nozzle dimensions: 1mmφ x 2mmL Load: 30Kg Heating rate: 3℃/min Generally, TPU refers to an elastomer with urethane bonds in the molecule, and polyurethane as a soft segment. It has a linear block copolymer structure with polyurethane as a hard segment. Generally, soft segments are obtained by reacting a polymer diol having hydroxyl groups at both ends with a diisocyanate, and hard segments are obtained by reacting a glycol or diamine with a diisocyanate. The TPU used in the present invention is soluble in MVC monomers and has a softening point in the range of 100 to 20°C,
In order to have such physical properties, it is necessary to select soft segments and hard segments. If there is too much hard and the molecular weight increases, solubility will be poor and the softening point of TPU will exceed 100°C, so it is necessary to limit the amount of hard segment used. Therefore, the TPU used in the present invention consists mostly of soft segments, and can contain a small amount of hard segments if necessary. Polyester diols, polyether diols, polyolefin diols, polylactone diols, and the like having a number average molecular weight of 500 to 10,000 are used as the polymer diol constituting the soft segment of TPU. Examples of polyester diols include glutaric acid, adipic acid, succinic acid, suberic acid, sebacic acid, oxalic acid, methyladipic acid, pimelic acid, azelaic acid, phthalic acid, terephthalic acid, isophthalic acid, maleic acid, and fumaric acid. Those obtained by an esterification reaction between a basic acid and a diol such as ethylene glycol, 1,4-butanediol, 1,6-hexanediol, propylene glycol, diethylene glycol, or neopentyl glycol are used. As the polyether diol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc. are used. As the polyoffine diol, polybutadiene diol or the like is used, and as the polylactone diol, polycaprolactone diol or the like is used. In the present invention, in order for the thermoplastic resin to have excellent performance, TPU using polyester diol, especially adipic acid-based polyester diol, is required.
is preferred. As the glycols and diamines constituting the hard segment of TPU, the diols shown as the raw materials for polyester diols and aliphatic and aromatic diamines such as ethylene diamine, propylene diamine, and xylene diamine are used. The diisocyanates that make up the soft and hard segments of TPU include 4,
4'-diphenylmethane diisocyanate, 4,
4'-diphenyl diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,5-naphthalene diisocyanate, xylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, etc. may be used alone or in combination of two or more. One suitable type of MVC soluble TPU that is effective in the present invention is Pandex T-5265 (trade name, manufactured by Dainippon Ink and Chemicals) (polyurethane mainly composed of adipic acid polyester diol and aliphatic diisocyanate; point, 53°C; weight average molecular weight, 120000), Pandex T-525
(softening point, 47℃), etc. In the present invention, the MVC soluble TPU is
Polymerization is initiated with 3 to 100 parts by weight, preferably 5 to 60 parts by weight, per 100 parts by weight of the MVC monomer. If the amount of MVC-soluble TPU is less than 3 parts by weight with respect to 100 parts by weight of MVC monomer, the coating film formed from the paint using the obtained polymer will not have satisfactory flexibility. On the other hand, if it exceeds 100 parts by weight, the coating film formed from the paint using the resulting polymer will be too soft and have insufficient mechanical strength. The preferred proportion of MVC-soluble TPU is 5 to 60% by weight based on 100 parts by weight of MVC monomer.
More preferably, it is 10 to 50% by weight. [Monomer copolymerizable with MVC] In the present invention, monomers copolymerizable with MVC include olefins such as ethylene and propylene, vinyl esters such as vinyl acetate, and n-
Vinyl ethers such as butyl vinyl ether,
Acrylic acid esters such as butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid 2
- Methacrylic acid esters such as ethylhexyl and the like can be mentioned. The amount used is preferably 50% by weight or less, more preferably 30% by weight or less in the MVC monomer. If the amount exceeds 50% by weight, the adhesion of the coating material made of the resulting polymer to the substrate will decrease. [Polymerization method] Methods such as solution polymerization using an organic solvent as a medium, suspension polymerization using water as a medium, and emulsion polymerization are adopted for producing the thermoplastic resin. The solvent used in solution polymerization may be any known solvent. For example, aromatic hydrocarbons such as toluene and xylene, ketones such as methyl ethyl ketone and cyclohexanone, ethers such as butyl cellosolove and butyl carbitol, and esters such as ethyl acetate, cellosolve acetate, butyl cellosolve acetate and butyl carbitol acetate are used alone. Alternatively, two or more types can be used in combination. Any known suspending agent or emulsifying agent may be used in suspension polymerization or emulsion polymerization. The charging ratio of organic medium or aqueous medium/(MVC soluble TPU+MVC monomer) in the production of thermoplastic resin is preferably 1/1 to 3/1. This is because if the ratio is less than 1/1, polymerization becomes unstable, and if the ratio exceeds 3/1, it is not economically advantageous. The oil-soluble polymerization initiator used in the production of the thermoplastic resin may be any known polymerization initiator. Examples include azo compounds such as azobisisobutylvaleronitrile, and organic peroxides such as lauryl peroxide, di-2ethylhexyl peroxydicarbonate, and t-butylperoxypivalate. The amount used is based on the MVC monomer at the time of preparation.
It is about 0.01 to 2% by weight. The polymerization temperature is 30° to 70°C, preferably 40° to 60°C. This is not industrially advantageous since the polymerization rate tends to slow down below 30°C. Moreover, if the temperature exceeds 70°C, the heat resistance etc. of the resulting polymer will deteriorate. In the present invention, known chain transfer agents such as trichlorethylene and mercaptoethanol may be used. [Conductive Filler] The conductive filler used in the present invention is a carbon-based conductive filler made of carbon black or graphite, and may be commercially available ordinary conductive carbon black or graphite. Examples of carbon black include furnace black, acetylene black, thermal black, channel black, etc., and as graphite, artificial or natural graphite powder can be used. Specific examples of commercially available carbon blacks include Ketuchen Black manufactured by Akzo Hemy, Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd., Acetylene Black manufactured by IBIDEN Co., Ltd., and Talka Black # manufactured by Tokai Carbon Co., Ltd. 4500 etc., and the graphite powder is natural graphite manufactured by Nippon Graphite Industries Co., Ltd.
CSSP, UFG-S2, UFG-S5 manufactured by Showa Denko K.K.
GP-100 manufactured by Kyowa Carbon Co., Ltd., SGP- manufactured by SEC Co., Ltd.
5, etc., and one or more of these can be used in combination. The blending ratio of the carbon-based conductive filler in the conductive paint of the present invention is preferably 10 to 60 parts by weight based on 100 parts by weight of the thermoplastic resin. If it is less than 10 parts by weight, the desired conductivity cannot be imparted to the coating film, and if it exceeds 60 parts by weight, carbon black or carbon black and graphite may fall off from the coating film, which is not preferable. [Solvent] The solvent for the thermoplastic resin in the coating of the present invention is aromatic hydrocarbons such as toluene and xylene, ketones such as methyl ethyl ketone and cyclohexanone, ethers such as butyl cellosolve and butyl carbitol, ethyl acetate, cellosolve acetate, and butyl cellosolve acetate. and butyl carbitol acetate, which can be used alone or in combination of two or more. There is no limit to the blending ratio of the solvent in the conductive paint of the present invention, but when the paint is used for screen printing, for example, the desired paint viscosity, e.g.
Thermoplastic resin with a viscosity of around 60000cps
A suitable amount is 150 to 900 parts by weight per 100 parts by weight. If the amount of solvent exceeds 900 parts by weight, the viscosity of the paint will be too low, and if it is less than 150 parts by weight, the viscosity of the paint will become too high, and in either case, the coating properties in screen printing will be poor. [Manufacture of conductive paint] The conductive paint of the present invention is a mixture of the thermoplastic resin with a carbon-based conductive filler and a solvent, or if necessary, a dispersant, an anti-settling agent, a lubricant, etc. The present invention is manufactured by uniformly mixing a small amount of the added material using an ordinary dispersion machine such as a ball mill or sand mill, and by such operation, the carbon-based conductive filler is dispersed in a solution in which a thermoplastic resin is dissolved in a solvent. of paint is obtained. The conductive paint of the present invention is not limited to use in membrane touch switches, but can also be used in other applications, such as antistatic and electromagnetic shielding. [Examples and Comparative Examples] The present invention will be explained in more detail with reference to Examples and Comparative Examples below. In addition, parts in each example represent parts by weight. Example 1 Pandex T-5265 (manufactured by Dainippon Ink and Chemicals Co., Ltd.) was placed in a stainless steel autoclave with an internal volume of 10.
670g, isophorone 2000g, butyl carbitol acetate 2000g, vinyl acetate 100g and 2,
After charging 13.3 g of 2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), the air in the gas phase was replaced with nitrogen, and then 2600 g of vinyl chloride was charged and polymerization was carried out at 38°C for 20 hours. Ivy. the result,
The polymerization yield based on vinyl chloride and vinyl acetate is
A solution was obtained containing a thermoplastic resin at 50% with the following composition: Polyurethane/vinyl chloride/vinyl acetate monomer Monomer unit Unit (weight ratio) = 55/62/5 A composition having the following composition was prepared using the above resin solution, and this was mixed in a ball mill for 24 hours. and got the paint. Paint composition: Thermoplastic resin 100 Kettchen Black (manufactured by Akzo Chemie) 25 Isophorone 150 Butycarbitol acetate 150 Soybean lecithin (manufactured by Kishida Chemical Co., Ltd.) 2 Comparative example 1 Thermoplastic resin shown in the paint composition of Example 1 Instead, a commercially available vinyl chloride/vinyl acetate copolymer was used in the same amount and a paint was obtained in the same manner. The paints obtained in Example 1 and Comparative Example 1 were applied onto a polyethylene terephthalate film (hereinafter referred to as the base material) using a doctor blade so that the thickness of the dried film was 50μ, and then The characteristics of the dried coating film were evaluated by the following method, and the results are shown in Table 1. (1) Surface resistance of the coating film The coating film on the substrate was left in an atmosphere of 23°C and relative humidity of 50°C for more than 24 hours, and a pair of gold-plated straight-ring electrodes (5 mm width, 35 mm length; weight 350gr)
were placed parallel to each other on the coating film with an interval of 35 mm, and the resistance value was measured using an electrometer with the surfaces sandwiched between the electrodes forming a square. (2) Adhesion Conforms to the JIS-5400 grid test method. Make a cross-shaped cut of 1 mm x 1 mm on the coating film on the base material, and
Evaluation is based on the number of areas where peeling occurred out of 100. (3) Flexibility Conforms to JISK-5400 bending resistance test method. Using 10 test pieces for each type of coating film, a 180° bending test was performed on each.
If there is no crack in the paint film on all sheets, it is evaluated as "good", and if there is a crack in the paint film on even one sheet, it is evaluated as "poor".
It was evaluated as follows.

[Table] (C) Effects of the Invention The conductive paint of the present invention has excellent adhesion to a base material made of polyester resin or polycarbonate resin, has appropriate flexibility, and has a desired surface resistance value. It has the property of forming a conductive coating and is industrially useful.

Claims (1)

[Claims] 1 Vinyl chloride monomer or a monomer mixture of vinyl chloride monomer and a monomer copolymerizable with it 100
The monomer or monomer mixture is added in the presence of 3 to 100 parts by weight of a thermoplastic polyurethane elastomer that is soluble in the monomer or monomer mixture and has a softening point of 20 to 100°C. A conductive paint made by dispersing carbon black or carbon black and graphite in a solvent solution of a thermoplastic resin obtained by polymerization.