JP2009073913A - Method for estimating physical strength of film from atomic force microscopic observation of aqueous resin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for estimating physical strength of a film from the microstructural observation of the surface of an aqueous polyurethane resin. <P>SOLUTION: The invention relates to a method for estimating physical strength of a film from the observation of the surface conditions of the film of an aqueous acrylic-modified polyurethane resin in air and in water by using atomic force microscope. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for predicting the physical strength of a film from atomic force microscope observation of the film obtained from a water-dispersed resin.

Recently, a 50% reduction in volatile organic compounds (VOC) has been required in the coating field. As a means for reducing this VOC, water-based resin coating is becoming increasingly important in the coating field of plastics, wood, metal, leather, concrete and the like.
Although the transition to water-based processing has been carried out in polyurethane resins as well, the present situation is that the technology has not been completed until the organic solvent type is replaced.
The main reason for this is that hydrophilicity must be imparted to the polyurethane molecules in order to disperse in water, which makes the polyurethane resin itself hydrophobic, inferior in water resistance and weather resistance.
Furthermore, the coating film made of an aqueous resin is formed because the particles dispersed in water adhere to each other as the dispersion medium water evaporates. In the organic solvent type, since it is completely dissolved, the formed film is nano-order smooth, but with an aqueous resin, it is not so smooth, and the film is formed while keeping the shape of the particles somewhat. .
Non-Patent Document 1 discloses that the film forming temperature and the surface shape are observed, and the boundary between the particle particles becomes unclear as the forming temperature increases.

D. Bhattacharjee, et al .: "Science and technology of polyurethane dispersions, Process and applications", PU magazine, vol 1 (2), p42 (2004)

However, the above document only discloses that an atomic force microscope is used for surface analysis of an aqueous polyurethane resin, and the relationship between the fine shape and the physical strength of the coating is not clarified.
An object of the present invention is to provide a method for predicting the physical strength of a coating film of an aqueous polyurethane resin by surface observation under specific conditions.

  That is, the present invention is a method for predicting the physical strength of a coating film from observation of the surface state of the aqueous acrylic modified polyurethane resin coating film in air and water using an atomic force microscope.

  According to the present invention, the water resistance of the coating can be predicted without being immersed for a long time. Furthermore, since the physical strength can be predicted by simple observation such as surface observation without performing a destructive test such as the tensile physical properties of the film, the optimum resin and the optimum film forming method can be easily established. Moreover, the shape of the coating film with good water resistance can be realized.

  As an atomic force microscope that can be used in the present invention, it is necessary to attach an apparatus capable of underwater observation. A preferred type is a closed loop type, but is not necessarily limited to this model. Examples of the probe used in the atomic force microscope include those composed of carbon nanotubes, platinum, iridium, cobalt, aluminum, diamond, silicon, silicon nitride, silicon carbide, and the like. The cantilever in the atomic force microscope preferably has a tip diameter of about 50 nm or less, and is selected according to the sensitivity of measurement. Further, the spring constant of the cantilever is about 0.01 to 80 N / m, and is selected according to the physical properties of the sample surface and the observation environment (in air or in water).

  Various physical strengths of the coating can be predicted. Among them, the great effect of the present invention is that water resistance can be predicted from observation of the surface state in water.

An actual prediction method will be described according to a specific example.
First, two types of acrylic urethane emulsions having different average particle diameters and a 9: 1 mixture thereof were prepared.
The surface state was observed by the method described below.

<Synthesis of allophanate-modified isocyanate>
In a 1000 ml reactor equipped with a stirrer, thermometer, condenser and nitrogen gas inlet tube, 800 g of hexamethylene diisocyanate (HDI), 200 g of methoxypolyethylene glycol (MePEG-400) having a number average molecular weight of 400, octylic acid 0.1 g of zirconium (manufactured by Daiichi Rare Element Chemical Industry) was charged and reacted at 110 ° C. for 6 hours. Next, 0.1 g of phosphoric acid was added, and a stop reaction was performed at 50 ° C. for 1 hour. The isocyanate content of the reaction liquid after the termination reaction was 35.7% by mass. This reaction solution was subjected to thin film distillation at 130 ° C. and 0.04 kPa to obtain allophanate-modified isocyanate (NCO-1). The yield of NCO-1 was 37.1%, the isocyanate content was 10.8% by mass, the viscosity at 25 ° C. was 200 mPa · S, and the free diisocyanate content was 0.1% by mass.

<Synthesis of emulsion>
<WAU-100>
In a 500 ml reactor equipped with a stirrer, thermometer, condenser and nitrogen gas inlet tube, 26.9 g of polycaprolactone ester diol (PCL) with a molecular weight of 2000, 3.6 g of dimethylolpropionic acid (DMPA), 37.8 g of n-butyl acrylate (MMA) and 0.025 g of methoxyquinone (MQ) as a polymerization inhibitor were charged, and the temperature was raised to 60 ° C. Next, 7.2 g of isophorone diisocyanate (IPDI) and 12.6 g of allophanated isoNCO-1 were charged, heated to 85 ° C., and reacted at the same temperature for 4 hours.
Next, 27.7 g of 2-hydroxyethyl methacrylate (2-HEMA) was added and heated at 85 ° C. for 3 hours, and the disappearance of the NCO group absorption peak was confirmed by FT-IR. The prepolymer solution was cooled to 30 ° C. or less, charged with 36.6 g of cyclohexyl methacrylate (CHMA), and mixed uniformly to obtain an acrylic monomer solution of urethane prepolymer.
The resulting acrylic monomer solution was charged with 2.0 g of triethylamine (TEA) to neutralize the carboxyl group, and then, with stirring, 322.3 g of water was charged and emulsified to obtain an aqueous dispersion.
Next, 0.6 g of ammonium persulfate (APS) was added to the reaction vessel, and radical polymerization was performed for 5 hours to obtain an acrylic-modified polyurethane aqueous emulsion. From the solid content measurement, it was confirmed that the polymerization of the acrylic monomer reached 99% or more, and the solid content was 35%. The average particle size measured with an electrophoretic scattering photometer ELS-800 manufactured by Otsuka Electronics was 100 nm.

<WAU-40>
An emulsion was obtained by the same method as WAU-100, except that TEA was increased to 2.7 g in order to reduce the particle size. The average particle diameter measured with the apparatus was 40 nm.

<WAU-BL>
It was prepared by blending 90 parts by weight of WAU-100 and 10 parts by weight of WAU-40.

<Preparation of observation sample>
It apply | coated so that the wet film thickness might be set to 100 micrometers on PET film, and it cured in the environment of 20 degreeC x 50% RH.
This sample was observed in air and pure water.

<Observation with atomic force microscope>
Atomic force microscope: Shimadzu Corporation, SPM-9600
Cantilever; AC240 (Olympus) frequency 70kHz
Spring constant = 2N / m

  The observation results of WAU-40 in air and water are shown in FIG. 1 and FIG. 2 of the drawings.

  The observation results of WAU-100 in the air and in water are shown in “FIG. 3” and “FIG. 4” of the drawings.

  The observation results of WAU-BL in the air and in water are shown in “FIG. 5” and “FIG. 6” of the drawings.

<Prediction of physical strength>
In the air and underwater irregularities of WAU-40 with an average particle size of 40 nm, the distance from valley to valley is 9.3 nm and 8.3 nm, respectively, and there is no significant difference. As a result, it is predicted that the swelling in water is small and the water resistance is good. Table 1 shows the numerical value of the surface state. This table also shows WAU-100 and WAU-BL.

The surface area in the table indicates a surface area corresponding to a projected area of 1 μm in length × 1 μm in width.
Ra is an index representing the level of surface roughness, and means that the larger the value, the rougher.

  On the other hand, the irregularities in the air and water in the WAU-100 air with an average particle size of 100 nm are 14.6 nm and 61.3 nm in the distance from the valley to the valley, respectively, and the distance in the water is larger than the distance in the air. It is also clearly larger. This shows that swelling has occurred, and its water resistance is expected to be considerably inferior to that of WAU-40.

  The physical strength of the coating is shown in Table 2.

<Measurement method of physical strength>
Elongation at break and adhesive strength were measured with a tensile tester.
The test piece was prepared by applying a brush on a waterproof material (Daiflex's OTAS ECO) with a brush so as to be 150 g / m ^2, and punching with a JIS No. 2 dumbbell from a sheet cured at 20 ° C. × 50% relative humidity for 1 week. went. The test piece thus prepared was subjected to a tensile test together with a waterproof material, and the elongation at break of the film was measured.
The adhesive strength was measured by measuring the adhesive strength between the waterproof material and the coating. For the test piece, a non-woven fabric was placed on the waterproof material, and the emulsion was impregnated from above until it reached the interface with the waterproof material. Thereafter, the sheet cured at 20 ° C. × 50% relative humidity for 1 week was cut into a width of 20 mm and subjected to a 180 ° peeling test. The peeling speed is 50 mm / min.
For water resistance, the sheet prepared by the above elongation test was immersed in warm water at 50 ° C. for 1 week, and a cross-cut test was performed immediately after the sheet was pulled up. The squares are 5 × 5 = 25 squares, and after peeling off with tape, the number of squares remaining on the sheet is displayed.

  From the above, it can be seen that the predicted content matches the actual measurement result.

WAU-BL is a 1: 9 blend ratio of WAU-40 and WAU-100, and the physical strength is estimated to be close to WAU-100 when considered normally.
However, in surface observation, it is close to the surface state of WAU-40, and it is predicted that the physical strength will be close to WAU-40, and the physical property measurement results support the prediction.

The observation result in the air of WAU-40 by an atomic force microscope is shown. The observation result in water of WAU-40 by an atomic force microscope is shown. The observation result in the air of WAU-100 by an atomic force microscope is shown. The observation result in water of WAU-100 by an atomic force microscope is shown. The observation result in the air of WAU-BL by an atomic force microscope is shown. The observation result in water of WAU-BL by an atomic force microscope is shown.

Claims (1)

A method for predicting the physical strength of a water-based acrylic-modified polyurethane resin film using an atomic force microscope from observation of the surface state in air and water.

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