JPH0116855B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aqueous dispersion composition, and more particularly to an aqueous dispersion composition of a tetrafluoroethylene/fluorovinyl ether copolymer, particularly a composition suitable for imparting non-stick properties by coating a substrate. relating to things. It is known to coat the surfaces of metals, ceramics, heat-resistant rubber, etc. with fluorocarbon polymers for various applications, such as polytetrafluoroethylene (PTFE) and tetrafluoroethylene/hexafluoropropene. Copolymers (FEP), tetrafluoroethylene/perfluoroalkyl vinyl ether copolymers (PFA), etc. are used to take advantage of their properties such as non-adhesiveness, heat resistance, chemical resistance, and low coefficient of friction. There is. PTFE-FEP is commercially available as an aqueous dispersion composition and is applied as a coating by spraying or dipping. Furthermore, FEP and PFA are used in electrostatic powder coating and are commercially available as powders of 5 to 150 μm. Examples of electrostatic powder coating include coatings on rolls of copying machines, as seen in, for example, JP-A-55-31494 and JP-A-58-24174. On the other hand, PTFE, FEP, and PFA can all be prepared as an aqueous dispersion, and examples are known in which an aqueous dispersion of FEP or PFA is mixed with an aqueous PTFE dispersion and used for coating. (For example, see Japanese Patent Publication No. 52-21531 and US Pat. No. 4,252,859).
However, there are almost no known examples of using PFA aqueous dispersions alone for coating purposes. For example, PFA aqueous dispersion is
It is prepared by the method described in No. The aqueous dispersion prepared according to the method of this patent is usually subjected to melt processing after separating the polymer and forming it into pellets or powder.
As shown in Figure 2, when this is applied to an aqueous dispersion composition, it can be applied only to an extremely thin film thickness, and if it is applied thickly, so-called mud cracks occur. Moreover, the surface of the coating film is also rough. The present invention aims to improve the drawbacks of such PFA aqueous dispersions, and the gist thereof is the general formula: (In the formula, X is H or F, n is a number from 0 to 7, m
is a number from 0 to 3. ) A copolymer of fluorovinyl ether and ^{tetrafluoroethylene represented} by particle size
An aqueous copolymer resin dispersion composition containing colloidal copolymer particles of 0.3 to 1 μm as a main component and stabilized with an anionic or nonionic surfactant. The composition of the present invention is composed of a colloidal tetrafluoroethylene/fluorovinyl ether copolymer aqueous dispersion, and can be coated in thick coats.
A smooth coating surface can be obtained. It is especially suitable for non-adhesive processing. Examples include fixing rolls for copying machines, food processing rolls, trays, and seasoning utensils. The colloidal copolymer particles, which are a requirement of the present invention, have an average particle diameter of 0.3 to 1 μm and a specific melt viscosity (MV) of 0.3 to 5×10 ⁴ poise. Only with these characteristics can the objectives of the invention be achieved. The composition of the present invention is characterized by thick coating processability and smoothness of the coating film, but the copolymer particles of the present invention are also unprecedentedly large for PFA, which is why they have a specific MV. Therefore, better thick coating processability and coating film smoothness are achieved. When coating with the composition of the present invention, a coating film with a thickness of at least 25 μm or more (usually 35 μm or more) can be formed in one coating. Also, the surface roughness is 0.5μm
Small as below. Usually, commercially available PTFE or
The reality is that an aqueous dispersion composition of FEP can only provide a coating film with a thickness of about 10 to 20 μm. With such a film thickness, for example, when processing a fuser roll for a copying machine, it is necessary to apply the coating to a thickness that is the sum of the required film thickness and the amount of surface polishing after painting, but usually 25 μm.
The above-mentioned film thickness is insufficient for the required film thickness. On the other hand, electrostatic coating using FEP or PFA powder produces coatings with a thickness exceeding 100 μm. but,
On the contrary, this is too thick, resulting in a large amount of cutting (resulting in loss of raw materials), which is uneconomical and requires a large number of man-hours. When the surface roughness of the coating film formed by the composition of the present invention is small, it is often possible to put it into practical use without surface polishing. As a result of a detailed study of both particle size and MV physical properties, the inventor found that MV was 0.3 to 5.
×10 ⁴ poise (preferably 0.4 to 3 × 10 ⁴ poise),
It has been found that an average particle diameter of 0.3 to 1 μm (preferably 0.5 to 0.8 μm) is most suitable for the above purpose, and the present invention has been completed. Regarding MV, if it is too high than the above range, the surface roughness will be large even if the particle size is large, and pine cracks will be likely to occur. In this case as well, we ended up having to remove a lot,
Uneconomical problems become a problem, and even the required film thickness cannot be obtained. Of course, if it is too low than the above range, the mechanical strength will be low and it will become brittle. Since the colloidally dispersed particles of the present invention are much larger than those commonly known, it is necessary to increase the viscosity of the composition to make it less likely to settle. Furthermore, it must have the property of being easy to redisperse even if it settles once. Therefore, anionic or nonionic surfactants or mixtures thereof are added to the composition. Types of nonionic surfactants typically include reactions between ethylene oxide as a hydrophilic part and compounds such as propylene oxide, saturated and unsaturated aliphatic alcohols, and alkyl phenols as hydrophobic parts. It is a product. For example, oxyethylene, oxypropylene block copolymer, HO(C ₂ H ₄ O) a-
(C ₃ H ₆ O)b-(C ₂ H ₄ O)c H (molecular weight 1000~
4000, 18≦a+b+c≦85),

[Formula] (d=4 to 20) is suitable. As the anionic surfactant, dialkyl sulfosuccinate, dodecylbenzenesulfonate, fatty acid soap, etc. can be used. In addition, water-soluble polymers or inorganic salts such as sodium alginate, polyvinyl alcohol, polyacrylates, and methylcellulose may be added to increase the viscosity of the composition. In addition, in order to further improve film-forming properties, water-insoluble organic solvents,
For example, it is also possible to disperse and emulsify benzene, toluene, xylene, etc. The nonionic or anionic surfactant used as a stabilizer is
20% by weight, preferably 4-10% by weight is suitable. If there is too much stabilizer, it will be difficult to volatilize during sintering and the coating performance will deteriorate. Furthermore, too much stabilizer and excessive thickener will make the painting process itself difficult. usually,
The viscosity of the composition of the present invention is 50 to 1000 at 25°C.
It is preferably adjusted to centipoise, preferably 100 to 400 centipoise. The content of the copolymer resin in the composition is preferably 20 to 65% based on the total weight of the composition. The composition of the present invention is first prepared by combining tetrafluoroethylene in an aqueous medium. (In the formula, n and m have the same meanings as above.) to perform emulsion polymerization, and then the obtained latex is concentrated, stabilized by adding a specified surfactant, and in some cases, further It can be manufactured by adding a thickener. In the emulsion copolymerization of the present invention, a so-called seed polymerization method is employed, and is characterized in that the final particle size is controlled by changing the amount of seeds. Furthermore, MV can be controlled by the amount of chain transfer agent, amount of initiator, reaction temperature, etc. As chain transfer agents, organic compounds containing hydrogen and present in substantially liquid form under the reaction conditions (e.g. methanol and ethanol) and alkyl halides (e.g. dichloromethane, trichloromethane, tetrachloroethane and chloroethane) may be used. . Examples of suitable polymerization initiators include water-soluble organic or inorganic peroxides such as disuccinic peroxide, ammonium persulfate, potassium persulfate, and the like. Additionally, reducing compounds such as ammonium sulfite, sodium bisulfite, sodium thiosulfate, etc. can also be used with the peroxides. Hereinafter, specific embodiments of the present invention will be illustrated by way of Examples. Example 1 First, a seed latex to be used for seed polymerization is synthesized by the method (1) (separately, a coating evaluation of the composition is carried out as Comparative Example 1). Thereafter, seed polymerization is performed by method (2). (1) In a stainless steel autoclave with an internal volume of 6 equipped with a temperature control jacket and a stirrer with anchor blades, add 2.9 g of deionized water, 400 g of trichlorotrifluoroethane as a dispersion stabilizer, 9.0 g of ammonium perfluorooctanoate, and chain transfer. Charge 2 ml of reagent grade methanol as a reagent, replace the inside of the tank for deoxidation twice with nitrogen gas and twice with TFE gas, and then charge 70 g of perfluor (propyl vinyl ether) (PPVE).
The temperature was raised to 65°C while stirring, and TFE gas was injected into the tank until the pressure within the tank reached 9.2 Kgf/cm ² .
Then, 100 ml of an aqueous solution containing 4.2 g of ammonium persulfate (APS) is added to start the reaction. During the reaction, keep the pressure inside the tank at 9.2Kgf/ ^cm2 .
Continuously supply TFE gas, reaction temperature is 65±1℃
is maintained. After 4.7 hours, the stirring is stopped, the autoclave is cooled to room temperature, and the gas is released back to atmospheric pressure. The copolymer concentration in the obtained latex is
The average particle diameter of the copolymer was 0.18 μm, the PPVE content in the copolymer was 3.2% by weight, and the MV of the copolymer was 1.0×10 ⁴ poise. (2) After charging the same amount of deionized water, trichlorotrifluoroethane, and ammonium perfluorooctanoate into the same autoclave as in (1), add reagent special grade methanol in the amount listed in Table 1 (11 ml),
The amount of Terrax synthesized in (1) in Table 1 (250
g) After preparation and deoxidation, add 70g of PPVE. Thereafter, 4.2g of APS is added and the reaction is carried out in exactly the same manner as in (1). The reaction temperature and reaction pressure are also the same. The reaction time, latex properties, etc. are as shown in Table 1. Next, after the reaction of the raw latex obtained in (2) is completed, the organic phase (trichlorotrifluoroethane and unreacted PPVE) is separated and transferred to a separate container, and polyoxyethylene octyl phenol ether (NOF) Add a nonionic surfactant aqueous solution containing 20% by weight of Nonion HS-208) to each raw latex.
Mix 30g. Keep the mixture at 30±1°C and let it stand. After standing still for about 20 hours, the supernatant layer of the mixture separated into a concentrated latex layer and a supernatant layer is removed to obtain a latex with a copolymer concentration of 60% or more. To further stabilize this concentrated latex, water and nonionic
Add HS208 and adjust the copolymer concentration to 50% by weight and nonionic surfactant to 5% by weight (based on polymer weight). The prepared composition is subjected to coating and coating evaluation as described below. A portion of the latex immediately after polymerization is evaporated to dryness, washed with acetone, and dried to powder. The MV was measured with this powder and also at 350℃.
Heat press for 15 minutes to create a film with a thickness of approximately 0.05 mm, and quantify the perfluor (propyl vinyl ether) content in the copolymer using infrared spectroscopy. The crack limit thickness of this example was 26 to 30 μm, and the surface roughness was 0.40 μm. On the other hand, in Comparative Example 1, the critical thickness was small and the surface roughness was rough (large). The effect of particle size is significant. Examples 2-5 In Example 2, the same seed latex used in Example 1 was used to carry out the seed polymerization. Example 3~
In Example 5, seed polymerization was carried out using part of the raw latex obtained in Example 1 as a seed (therefore, as a result, seed polymerization was carried out twice). The amounts of methanol and ammonium persulfate used are as listed in Table 1, and all conditions other than those listed in Table 1 are the same as in Example 1. As shown in Table 2, all had excellent coating film properties. Example 6 In the method of step (1) of Example 1, deionized water, trichlorotrifluoroethane, ammonium perfluorooctanoate, and PPVE were used in the same amounts, and as a chain transfer agent, reagent special grade was used instead of methanol. 66g of dichloromethane was used. The polymerization temperature was 35° C., and the reaction was started by adding 50 ml of an aqueous solution containing 4.2 g of ammonium persulfate, followed by the addition of 50 ml of an aqueous solution containing 2.3 g of sodium sulfite.
During the reaction, tetrafluoroethylene was supplied so as to keep the internal pressure at 9.2 Kgf/cm ² and the polymerization temperature was maintained at 35±1°C. After 9.6 hours, the reaction was terminated in the same manner as in step (1) of Example 1, and a latex with a polymer concentration of 19.0% by weight and an average particle size of 0.18 μm was obtained, and the MV of the copolymer was 3.3×10 ⁴ poise. , the PPVE content was 2.7%. Furthermore, using 250 g of this latex as a seed, the same amount of deionized water as above, trichlorotrifluoroethane, ammonium perfluorooctanoate,
The mixture was charged into an autoclave with PPVE, and then 90 g of dichloromethane was added as a chain transfer agent, and the same amounts of ammonium persulfate and sodium sulfite as above were added to carry out seed polymerization. reaction pressure,
The reaction temperature was the same as for the synthesis of the seed latex. After 14 hours, the latex had a polymer concentration of 18.7% and an average particle size of 0.35 μm. The MV of the copolymer was 2.1×10 ⁴ poise, and the PPVE content was 3.0% by weight. The raw latex thus obtained was subjected to organic layer separation, concentration, stabilization, and adjustment in the same manner as in Example 1, and the coating and coating film were evaluated. The crack thickness limit was 30 to 35 μm, and the surface roughness was 0.50 μm. Comparative Examples 1 to 5 Comparative Example 1 is the seed latex composition of Example 1, and Comparative Examples 2 to 3 are seed latex compounds without seed polymerization.
This is a method for producing seed latex in Example 1 in which the amount of methanol was changed to change the MV. Comparative Example 4 used the raw latex of Comparative Example 2, and Comparative Example 5 used the raw latex of Comparative Example 1, and seed polymerization was carried out under the conditions shown in Table 1 according to Example 1. The physical properties of the coating film are as shown in Table 2, and Comparative Example 4
Even if the particle size is large, the MV is too high and the surface roughness is large. Comparative Example 5 has good crack limit film thickness and surface roughness, but in this case,
This is probably because the MV is too small, but the coating film strength is low and it is almost impractical. Comparative Example 6 Seed latex used in Example 6 (average particle size
0.18 μm, MV 3.3×10 ⁴ poise, PPVE content 2.7% by weight) was separated, concentrated, stabilized, and adjusted in the same manner as in Example 1, and then painted and evaluated. The crack limit thickness is 20~25μm, and the surface roughness is
It was 0.80 μm. In addition, in Examples 2 to 6 and Comparative Examples 1 to 5, the organic layer separation, concentration, stabilization, and adjustment were performed as described in Example 1, and the coating and coating film evaluation were performed under the same conditions. <Specific melt viscosity> Using a Koka type flow tester made by Shimadzu Corporation, 2.0 g of copolymer powder was loaded into a cylinder with an inner diameter of 11.3 mm, and after keeping at a temperature of 380°C for 5 minutes, the inner diameter was 2.1 mm under a piston load of 7 kg. mm, extrusion through an orifice with a length of 8 mm, extrusion speed (g/min)
The specific melt viscosity (poise) was determined by dividing 53150 by . <Average particle size> Regarding the latex immediately after the completion of polymerization of the concentrate,
Photographs were taken with a transmission electron microscope, and the directional length and diameter of about 100 to 400 particles were measured to determine the average length diameter. <Fluorovinyl ether content in the copolymer> Regarding perfluorinated (propyl vinyl ether) in the copolymer, the above-mentioned film was measured by infrared spectroscopy to determine the absorbance at 995 cm ^-1 relative to the absorbance at 2360 cm ^-1 .
It was determined by multiplying the absorbance ratio by 0.95 (see JP-A-56-92943). <Painting test> The prepared aqueous dispersion composition was coated with a width of 5 cm and a length of 40 cm.
Spray painting on a 1 mm thick aluminum plate (previously cleaned with acetone and deoiled). Spray gun nozzle diameter is 0.8~1.1
mm, and the air pressure is approximately 3Kg/cm ² . At this time, the amount of the composition sprayed on each part of the aluminum plate is changed appropriately so that the thickness after firing is 10 to 50 μm. After spraying, infrared drying oven (approx. 100℃)
Pre-dry for 10 minutes, then place in an electric furnace controlled at 400°C and bake for 20 minutes. Immediately after firing, remove from the furnace and allow to cool to room temperature. <Evaluation of paint film> Measure the thickness of the paint film using a surface film thickness meter. As the film thickness increases, mound cracks are observed, but the maximum film thickness without mound cracks is defined as the crack limit thickness. Universal surface profile measuring device for surface roughness (Kosaka Institute Co., Ltd.)
Measured using SE-3C). Since the surface roughness varies depending on the film thickness, we will compare the film thickness of approximately 20 μm.

【table】

【table】

[Table] ** The resulting paint film developed pine cracks after a few days.

Claims (1)

[Claims] 1. General formula: (In the formula, X is H or F, n is an integer of 0 to 7,
m is an integer from 0 to 3. ) A copolymer of fluorovinyl ether and ^{tetrafluoroethylene represented} by particle size
An aqueous copolymer resin dispersion composition containing colloidal copolymer particles of 0.3 to 1 μm as a main component and stabilized with an anionic or nonionic surfactant. 2. The composition according to claim 1, wherein _the fluorovinyl ether is _C3F7OCF = _CF2 . 3 The average particle size is larger than 0.5 μm and the specific melt viscosity is
The composition according to claim 1, which has a poise of 0.4 to 3.0×10 ⁴ poise. 4. The composition according to claim 1, having an average particle size of 0.6 to 0.8 μm. 5. The composition according to claim 1 for non-adhesive coating.