JPH04349306A - Manufacture of antistatic vinyl chloride sheet - Google Patents

Abstract

PURPOSE:To form a conductive layer on the surface layer of a vinyl chloride sheet. CONSTITUTION:After acrylic acid and/or methacrylic acid or their solutions are applied on the surface of a vinyl chloride sheet, the radiation of an electron beam from the coated surface side graft-polymerizes a monomer on the surface of the vinyl chloride sheet, followed by washing and treating with a solution of sodium hydroxide or potassium hydroxide, so that a conductive layer of sodium carboxylic acid salt or potassium salt is formed on the surface layer.

Description

[Detailed description of the invention]

001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a vinyl chloride sheet which is prevented from being electrostatically charged by forming a conductive layer of an ion-mobile sodium or potassium carboxylic acid salt on its surface.

002]

[Prior Art] In precision industries that use plastic parts, such as the electronic industry and the bio-industry, static electricity can destroy semiconductor elements or attract dust and dirt, reducing yields. Although it has become a major problem, this problem of static electricity does not only occur when plastic parts are used in products, but also when plastic materials are used for floors, partitions, blinds, chair skins, document covers, etc. in factories and laboratories. It also occurs when used. For this reason, when plastics are used for product parts and interiors of factories and research institutes, they are treated with antistatic treatment.

[003] By the way, vinyl chloride sheets are the most commonly used plastics for the above purposes, and antistatic treatments for them include (1) a method of kneading a surfactant into the sheet, and (2) a method of kneading a surfactant into the sheet. ) method of applying surfactant to the sheet surface, (3) method of kneading conductive filler such as metal or metal oxide into the sheet, (4) method of applying metal or metal oxide to the sheet surface. The method used was to form a coating film in which conductive filler such as material was dispersed.

004

[Problem to be solved by the invention] However, (1)
In this method, the surface resistivity cannot be lowered to 1011 Ω/cm2 or less, and very good antistatic properties cannot be obtained. Furthermore, even with method (2), antistatic properties comparable to those of method (1) were obtained, and in addition, the durability was inferior to method (1). Furthermore, method (3) is inferior in transparency and light transmittance, cannot be applied to the production of colorless transparent sheets, and is expensive. Method (4) is (3
Since the conductive layer is thinner than the method described in ), the transparency, light-transmitting coating film, and price are improved, but there is a problem that the coating film is easily peeled off. The present invention provides a method for producing an antistatic vinyl chloride sheet that eliminates these drawbacks.

005]

[Means for Solving the Problems] The present invention involves coating the surface of a vinyl chloride sheet with one or both of acrylic acid and methacrylic acid, or a solution containing 25 wt% or more of these, and then applying an electron beam to the surface of the vinyl chloride sheet for 20 minutes. The coating monomer is graft-polymerized onto the vinyl chloride sheet by irradiation of ~100 kGy, and then the monomer or solution remaining on the surface of the vinyl chloride sheet is washed, and the vinyl chloride sheet is treated with sodium hydroxide or potassium hydroxide. The treatment was carried out with an aqueous solution of

006]

[Operation] After coating the surface of a vinyl chloride sheet (hereinafter referred to as vinyl chloride sheet) with one or both of acrylic acid and methacrylic acid, or a solution containing 25 wt% or more of these, when irradiating an electron beam from the coated surface side, Since the double bond of the acryloyl group of acrylic acid or the methacryloyl group of methacrylic acid is graft-polymerized onto the vinyl chloride sheet, a graft layer having carboxyl groups is formed on the surface of the vinyl chloride sheet. After washing the vinyl chloride sheet on which the graft layer has been formed to remove the monomer or solution remaining on the surface, the vinyl chloride sheet is treated with an aqueous solution of sodium hydroxide or potassium hydroxide. The carboxyl group of reacts with the alkali hydroxide to form an alkali metal carboxylic acid salt (
-COO-M+, M is Na, K).

[007] Since the alkali metal ions such as Na+ and K+ in this alkali metal carboxylate salt can freely move in the layer where the alkali metal salt carboxylate is present in the graft layer, the electrical resistance of the surface of the PVC sheet is reduced. However, static electricity leaks easily and antistatic properties are imparted. In the present invention, the alkali metal ions are easily moved because acrylic acid and methacrylic acid are graft-polymerized, so that the alkali metal carboxylic acid salts are chained together.

[008] In addition to the main resin of the vinyl chloride sheet of the present invention, which is a vinyl chloride homopolymer, a copolymer of vinyl chloride and a monomer copolymerizable with vinyl chloride such as vinyl acetate ethylene, a vinyl chloride homopolymer, etc. Contains blends of PVC with polymers that are compatible with PVC. Furthermore, although a plasticizer is usually added to vinyl chloride, it is also possible to use one without this plasticizer. Furthermore, if necessary, epoxy compounds, stabilizers, pigments, ultraviolet absorbers, antioxidants, etc. may be added, but the vinyl chloride sheet of the present invention does not care whether or not these are added. .

[009] The monomer applied to the surface of the vinyl chloride sheet must have an acryloyl or methacryloyl group, which is an electron beam-reactive functional group, and a carboxyl group, which forms an alkali metal carboxylate salt by reaction with an alkali hydroxide. However, even if they have these functional groups, substances other than acrylic acid and methacrylic acid, such as the following, cannot be used because graft polymerization does not occur sufficiently. CH2=C(CH3)-CO-OCH2CH2-RR;
-OCO(CH2)2-COOH-OCOC6H4
-COOH -OCH2CH2-COOH

Acrylic acid and methacrylic acid may be applied alone or in combination. The object of the present invention can also be achieved by applying the solution as a solution. In this case, the concentration of acrylic acid or methacrylic acid is 25 wt% individually or in total.
It is necessary to do more than that. If the concentration is lower than this, sufficient antistatic properties cannot be obtained because graft polymerization does not occur sufficiently. This is because if the amount of graft polymerization is small, the concentration of carboxyl groups introduced into the surface layer of the PVC sheet will be low, and the concentration of the alkali metal carboxylate produced by alkali treatment will also be low, and the electrical resistance will not decrease sufficiently. It is from.

[011] As a solvent for solutions of acrylic acid, methacrylic acid, etc., any solvent can be used, including water, organic solvents, monomers, oligomers, and polymers. - solubility in
It is important to consider factors such as swelling ability. Even if acrylic acid or methacrylic acid is applied as it is or as a solution, a polymerization inhibitor such as Mohr's salt may be added to suppress homopolymerization of acrylic acid or methacrylic acid.

Acrylic acid, methacrylic acid, and their solutions may be applied to the vinyl chloride sheet by any known method, such as a spray method, curtain flow method, or roll coating method.

[013] Graft polymerization of acrylic acid or methacrylic acid onto a vinyl chloride sheet can prevent static electricity from being charged if it is carried out only on the surface layer, so the electron beam irradiation is generally called a low-energy type. An electron beam of less than 300 keV is sufficient, but electron beams with higher energies can also be used, and gamma rays can also be used.

[014] The dose of the irradiated electron beam is 20 to 100 kGy, but if it is less than 20 kGy, acrylic acid and methacrylic acid will not be graft-polymerized sufficiently. This is because the concentration becomes low and the concentration of the alkali metal carboxylate salt after treatment with an aqueous sodium hydroxide or potassium hydroxide solution is insufficient, so that the electrical resistance does not decrease sufficiently. On the other hand, if it exceeds 100 kGy, the PVC sheet will deteriorate, turn yellow, and its commercial value will be greatly reduced, and the surface will develop tacking properties.

After electron beam irradiation, the monomer and its solution remaining on the surface of the vinyl chloride sheet are washed away, and treated with an aqueous solution of sodium hydroxide or potassium hydroxide. The solution after electron beam irradiation contains homopolymers of acrylic acid and methacrylic acid, so if they are not washed and removed, tacking will remain and the acid will be carried into the next alkaline treatment step. This results in a decrease in pH and contamination of foreign substances, making it difficult to form alkali metal salts. Water is usually used for washing, but organic solvents may also be used.

One of the reasons why the alkali treatment after washing is limited to an aqueous solution of sodium hydroxide or potassium hydroxide in the present invention is that unless the alkaline aqueous solution is highly basic and highly concentrated, the carboxyl group can be efficiently converted to an alkali metal carboxylate. This is because it cannot be changed to In other words, there are various alkaline metal compounds, but the ones that are highly basic and highly water-soluble are hydroxides, and the most alkaline among them are alkali metal hydroxides. This is because potassium oxide is highly basic and highly water soluble.

Another reason is that the radius of hydrated ions is small and the ionic conductivity is excellent. The surface resistivity of the vinyl chloride sheet after alkali treatment depends on the hydrated ionic radius of the metal ion, and the smaller the hydrated radius, the smaller the steric hindrance, which facilitates movement and facilitates ionic conductivity. For this reason, the surface resistivity becomes smaller, making it easier to leak current.
Antistatic property increases. Among alkaline metal compounds, those with a small hydrated ionic radius are alkali metal hydroxides, and among these, sodium hydroxide and potassium hydroxide have a small hydrated ionic radius and are inexpensive. . Rubidium hydroxide can also be used, but it is expensive and has practical problems.

In the alkali treatment, the higher the concentration and temperature of sodium hydroxide or potassium hydroxide, the faster the carboxyl group can be converted into an alkali metal carboxylate. The treatment method does not matter as long as it brings a water-soluble alkali into contact with the surface of the PVC sheet, but for practical purposes, dipping, spraying, roll coating, etc. may be used. .

019]

[Example] Various monomers or their solutions were coated on the surface of PVC sheets with different amounts of plasticizer added using bar coater #20, and an electron beam was applied from the coated surface side at an accelerating voltage of 200 kV.
Irradiation was performed while varying the dose. Thereafter, the PVC sheets were washed with water to remove the solution remaining on the surface, immersed in alkaline aqueous solutions (40 DEG C.) of various concentrations for 1 minute, washed with water, and dried.

After drying, the surface specific resistance (JIS
K 6911) and charging voltage (JISL 1094) were measured at a temperature of 23° C. and a humidity of 50%. In addition, the transparency of the sheet was visually evaluated. Examples are shown in Table 1 and Table 2, Table 3
, Table 4 shows comparative examples along with processing conditions. In addition, among the monomers used in the comparative example, monomers A, B, and C are as follows. Monomer-A; CH2=C(CH3)-CO-OCH2CH2-OCO
(CH2)2-COOH Monomer-B; CH2=C(CH3)-CO-OCH2CH2-OCO
C6H4-COOH Monomer-C; CH2=C(CH3)-CO-OCH2CH2-OCH
2CH2-COOH

021]

[Table 1]

022]

[Table 2]

023]

[Table 3]

024]

[Table 4] (Note 1) Items marked with * had a residual acid odor. (Note 2) Items marked with ★ were yellowed. (Note 3) Tacking was observed on the surface of all opaque products.

025]

As described above, the method of the present invention involves graft polymerizing acrylic acid or methacrylic acid on the surface layer of a PVC sheet, and then treating it with alkali to form a conductive layer on the surface layer. The surface specific resistance of the sheet is 1011Ω/cm2
It can be: Furthermore, compared to forming a conductive layer on the surface of a PVC sheet by forming a coating film filled with a conventional conductive filler, processing costs are lower and the transparency of the PVC sheet is maintained. Furthermore, since the conductive layer is chemically bonded to the PVC sheet, it will not peel off, and the physical properties of the PVC sheet are
There is almost no change even if a conductive layer is formed.

Claims (1)

[Claims] [Claim 1] Acrylic acid on the surface of vinyl chloride sheet,
one or both of methacrylic acid, or 25
After applying a solution containing % wt% or more, 20 to 100 kGy of electron beam is irradiated from the coated surface side to graft-polymerize the coated monomer onto the vinyl chloride sheet, and then the monomer remaining on the surface of the vinyl chloride sheet or A method for producing an antistatic vinyl chloride sheet, which comprises washing the solution and treating the vinyl chloride sheet with an aqueous solution of sodium hydroxide or potassium hydroxide.