JPH0516321B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention relates to an improved method of manufacturing painted formwork plywood. (Prior art and its problems) In recent years, as the raw wood situation has worsened, relatively low-quality wood has come to be used for formwork plywood. When form plywood manufactured from such low-quality wood is used as concrete formwork for civil engineering and construction work, problems such as poor curing of the concrete and contamination of the concrete surface with wood pigments occur. Furthermore, recently, there has been an increase in the use of a construction method called exposed concrete construction, mainly in the construction of public facilities, which requires a smooth concrete surface.
Formwork plywood manufactured from low-grade wood has poor surface smoothness, which is also a problem. In order to solve these problems, in recent years the surface of formwork plywood has been painted with acrylic paint or urethane paint.
So-called painted formwork plywood began to be manufactured and marketed,
The amount also tends to increase year by year. However, when manufacturing coated form plywood by coating the surface of form plywood with acrylic paint or urethane paint, the following problems arise. (1) When painting formwork plywood with acrylic paint or urethane paint, the coating film is thin with one coat, so it usually takes two coats.
It requires ~3 coatings and must be dried after each coating, making the work complicated and resulting in poor work efficiency. (2) Since acrylic paints and urethane paints are thermoplastic, they are usually dried at room temperature, which takes a long time to dry. (3) Acrylic paints and urethane paints contain organic solvents, and since these organic solvents volatilize during the drying process, equipment for recovering the volatilized organic solvents is also required as a pollution control measure. (4) Acrylic paints and urethane paints belong to the category of expensive paints, so using such paints on painted plywood, which is consumed in large quantities, would be costly. The inventors of the present invention solved these problems and, as a result of intensive studies on manufacturing coated formwork plywood with good workability and productivity and low cost, developed a modified synthetic rubber latex and a heat-curable amino resin. It was discovered that this problem could be solved by using a paint containing a modifier and a modifier, and the patent was filed as Japanese Patent Application No. 1983-283841. However, when painting formwork plywood is manufactured using a paint made of the above-mentioned modified synthetic rubber latex, heat-cured amino resin, and modifier, a coating film of sufficient thickness may not be obtained with one application. In this case, one more application is unavoidably necessary. [Means for solving the problem] As a result of further studies to ensure that the present invention can always obtain a coating film of sufficient thickness with one application, it has been found that adding an appropriate amount of filler to the above paint produces good results. The present inventors have discovered that the following can be obtained, and have completed the present invention. That is, the method for producing painted formwork plywood of the present invention comprises a compound having a conjugated diene bond (first component), a vinyl monomer (second component), a carboxyl group, an N-methylol group, a glycidyl group, a hydroxyl group, an amino group,
A reactive monomer (tertiary
After applying a composition (hereinafter referred to as the coating composition) consisting of a modified synthetic rubber latex made of a copolymer with a thermosetting amino resin, a modifier, and a filler (hereinafter referred to as the coating composition) to one or both sides of the formwork plywood. , which is characterized by being cured by heating. (Specific Means for Carrying Out the Invention) The present invention will be explained in detail. The modified rubber latex used in the present invention is manufactured by the same method as the modified synthetic rubber latex used in the inventions described in Japanese Patent Application No. 165938/1982 and Japanese Patent Application No. 283841/1983, which were previously filed by the present inventors. I can do it. That is, the first component in the production of the modified synthetic rubber latex of the present invention is a compound having a conjugated diene bond, and butadiene or isoprene is mainly used. The vinyl monomer (second component) is one that can be copolymerized with the first component and the third component, such as styrene, methyl acrylate, methyl methacrylate, and acrylonitrile. The amount of the compound having a conjugated diene bond (first component) in the modified synthetic rubber latex is 20 to 80% by weight based on the total amount of this first component and the above-mentioned vinyl monomer (second component). %) is preferred. If the first component is less than 20%, the coating film of painted formwork plywood manufactured using the latex will become too hard and cracks will easily occur on the coating surface;
Exceeding this is not preferable because the coated surface of the manufactured painted formwork plywood becomes too soft and easily scratched. Examples of the reactive monomer (third component) having a crosslinkable reactive group in its side chain include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, etc., as monomers having a carboxyl group. - N for monomers with methylol groups
-Methylol acrylamide, N-methylolmethacrylamide, etc., and their ethers; monomers having a glycidyl group include glycidyl acrylate, glycidyl methacrylate, acrylic glycidyl ether, etc., and monomers having a hydroxyl group include allyl alcohol, 2 -Hydroxyethyl methacrylate, 2
-Hydroxyethyl acrylate, 2-hydroxypropyl methacrylate, 2-hydroxypropyl acrylate, monoallyl ether of polyhydric alcohol, etc. Monomers having amino groups include N,N-dimethylaminoethyl acrylate, vinylpyridine, tert- Examples include butylaminoethyl methacrylate, monomers having an amide group include acrylamide, methacrylamide, maleamide, etc., and acid anhydrides include itaconic anhydride, maleic anhydride, etc. The ratio of the third component in the modified synthetic rubber latex is 0.1 to the total amount of the first and second components.
~20% is preferred. If it is less than 0.1%, the crosslinking of the modified synthetic rubber latex will be insufficient and a strong coating film will not be obtained on the formwork plywood, and if it exceeds 20%, the stability of the latex during polymerization will be poor and a good latex will not be obtained. This is because it cannot be obtained. Note that the higher the solid content concentration in the modified synthetic rubber latex used in the present invention, the lower the moisture content. In the process of heat-pressure curing of the composition to form a coating film, a portion of excessive moisture is locally or generally sealed within the coating film, leaving only that area in a sticky state. It is a term used to refer to cloudy areas, where the acid and alkali resistance of the coating film decreases.) It is preferable in that it can prevent this, but modified synthetic rubber latex is usually commercially available with a solid content concentration of 40 to 60%. Therefore, in the present invention, this commercially available product can be used as is. Next, examples of the heat-curable amino resin (hereinafter simply referred to as amino resin) used in the present invention include urea resin, melamine resin, and co-condensed resin adhesives thereof. Formaldehyde (F) and urea are used as urea resins.
(U) is condensed with a molar ratio of 1.0 to 3.0 as F/U, and as a melamine resin, the molar ratio of formaldehyde (F) and melamine (M) as F/M is 2.0 to 3.5. A condensed product is used. Further, these amino resins are preferably modified using a modifier such as polyvinyl alcohol, carboxymethyl cellulose, or hydroxyethyl cellulose. The reason is that an amino resin with an appropriate viscosity can be obtained by modifying it.
This is because when the composition used in the present invention is applied to formwork plywood, a coating film with an appropriate thickness is formed. The solid content concentration in the amino resin is preferably 60% or more, more preferably 60 to 80%. If it is less than 60%, the water content in the coating composition will increase, and during the heating and curing process of the coating composition, local curing failure, commonly known as clouding, will likely occur, and the alkali resistance and mortar resistance of the affected areas will decrease. Therefore, it is not desirable, and on the contrary, 80
Amino resins with a solid content concentration of more than 1% are difficult to manufacture and are also inconvenient to handle. In the present invention, the ratio of the modified synthetic rubber latex to the amino resin is such that the solid content of the amino resin is 50 to 400 parts by weight per 100 parts by weight of the solid content in the modified synthetic rubber latex. It is preferable that More preferably, it is 100 to 300 parts.
If the amount of amino resin is higher than the above ratio, the coating film of the resulting painted formwork plywood will become too hard, cracks will occur on the coating surface, the coating layer will become brittle, and the weather resistance will tend to decrease. On the other hand, if the proportion of amino resin is too low, not only will the coating surface become too soft and easily scratched, but the coating will also have poor chemical resistance such as acid resistance and alkali resistance, and will therefore withstand concrete mortar. It is not preferable because sufficient coating performance cannot be obtained. Modifiers used in the present invention include, for example, polyoxyethylene noniphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene oleyl ether, Ethers such as oxyethylene lauryl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether, polyoxyethylene lanolin alcohol ether, polyoxyalkylamine ether, polyoxyethylene distearate, poly Esters such as oxyethylene lanophosphate, fatty acid diethanolamides or sulfonated or phosphate compounds of these compounds, dimethylpolysiloxane silicone, methyl silicone, dimethyl silicone, methylhydrogen polysiloxane silicone, methyl phenyl silicone, fluorosilicone and other silicone compounds, and compounds in which the methyl group of dimethylpolysiloxane is α-methylstyrenated, α-olefinized compounds, polyetherified compounds, trifluoroalkylated compounds, amidated compounds, mercapto-ized compounds, Examples include epoxidized compounds, carboxylated compounds, and polyolefin wax emulsions such as polyethylene wax and polypropylene wax, and one or more of these compounds can be used. The amount of the modifier added is preferably 0.2 to 10 parts per 100 parts by weight of the total solid content in the synthetic rubber latex and solid content in the amino resin. If it is less than 0.2 parts, it is undesirable because the alkali resistance of the painted formwork plywood and the mold releasability between the painted formwork plywood and cement mortar will deteriorate, and if it exceeds 10 parts, it will not be possible to obtain a strong coating film. However, this is not preferable because it causes an increase in cost and is economically disadvantageous. There are organic and inorganic fillers, but the fillers that can be used in the present invention are water-insoluble,
Examples of organic materials include wood flour and coconut powder, and examples of inorganic materials include kaolin, talc, clay, calcium carbonate, and gypsum. These are used after being crushed to a particle size of 200 mesh or less. Note that grain flour such as wheat flour is disadvantageous because the viscosity of the coating composition becomes too high. The amount of filler added varies somewhat depending on the type of filler, but it is 20 parts per 100 parts of the total solid content in the modified synthetic rubber latex and solid content in the amino resin.
~200 parts is preferred. If the amount is less than 20 parts, it is not appropriate because a coating film of an appropriate thickness may not be obtained when the composition used in the present invention is applied to formwork plywood.On the other hand, if it exceeds 200 parts, the filler Excessive amount is not preferable because the coating film becomes brittle. In the present invention, a coating composition is prepared by mixing a modified synthetic rubber latex, an amino resin, a modifier, and a filler at room temperature, but there is no particular restriction on the order in which the above-mentioned four components are mixed. For example, after mixing a modified synthetic rubber latex, an amino resin, and a filler, a modifier may be added thereto, or after mixing either a modified synthetic rubber latex or an amino resin with a modifier, both of them and There is no problem even if it is mixed with a filler. Incidentally, in order to obtain a beautiful painted formwork plywood, it is preferable to add a small amount of a known pigment made of titanium or iron oxide to this coating composition. The amount of pigment added varies depending on the hue of the pigment, but is generally 1 to 5 parts per 100 parts of the coating composition. The thus obtained coating composition further contains conventionally known curing accelerators for amino resins (hereinafter simply referred to as curing accelerators) such as ammonium chloride, ammonium sulfate, ammonium nitrate, etc.
It is preferable to add 1 to 3 parts per part. The coating composition to which the curing accelerator has been added is applied to one or both sides of the formwork plywood as a base material as soon as possible. Whether to apply single-sided coating or double-sided coating depends on the intended use of the manufactured coated formwork plywood. The amount of coating composition applied to the form plywood is usually 50 to 400 g/m ² , preferably 200 g/m 2 per surface area of the form plywood.
~300g/ ^m2 . If the coating amount is less than 50g/ ^m2 , a sufficiently thick coating layer will not be formed;
If it is more than m ² , the thickness of the coating layer becomes too thick and the coating composition becomes wasted, leading to an increase in cost, which is not preferable. As the coating method, a known roll coater method is commonly used. Therefore, since it is preferable to cure the coating composition applied to the form plywood under pressure in order to obtain a smooth coating surface and a strong coating film, it is usually cured under hot pressure using a hot press. The material is heat-hardened by compaction or hot rolling using heater rolls, but prior to heat-hardening, it is preferable to perform preliminary drying at a temperature lower than the heat-hardening temperature. In other words, if the paint composition is applied to the formwork plywood and then suddenly hot-pressed, since the paint composition still has fluidity, it will flow out of the formwork plywood and cause an underapplication, resulting in a uniform coating. It is not possible to obtain a continuous coating film, and furthermore, it is not possible to obtain a coating film of an appropriate thickness. Further, the paint composition flowing out from the formwork plywood not only results in loss but also causes staining of equipment such as hot presses and heater rolls, which is inconvenient. Pre-drying forms a film on the surface of the coating composition applied to the formwork plywood, and the viscosity of the coating composition also increases significantly, so it is possible to apply the coating to an appropriate thickness without causing the above problems during hot pressing. It is possible to obtain a film. Pre-drying temperature is preferably 40 to 80°C. At temperatures below 40°C, it takes a long time for the surface of the coating composition to dry and form a film. On the other hand, temperatures exceeding 80° C. are unsuitable because the temperature is too high and there is a risk that the surface of the coating composition will be completely cured during pre-drying. The pre-drying time depends on the pre-drying temperature, but it is usually 5.
Performed in ~30 minutes. As mentioned above, the coating composition applied to the formwork plywood can be heated and cured using a hot press or a heater roll after preliminary drying to obtain coated formwork plywood. More preferred. Even if the formwork plywood has a slight problem with smoothness due to some distortion on the surface, the distortion can be corrected by hot pressure compression, so the surface can be made smooth and a dense coating surface can be obtained. Because it can be done. Heating compression pressure is 10~30
Kg/cm ² ·G is appropriate. If the pressure is less than 10Kg/ ^cm2・G, the pressure is insufficient, and if the pressure is higher than 30Kg/ ^cm2・G, the thickness of the wooden part, which is the base material of the painted formwork plywood, will decrease due to compression, so make sure to thicken it in advance. It is necessary and economically disadvantageous. The conditions for hot compression are usually 110 to 130°C and 30 to 180 seconds. Since the heater roll rolls at a pressure of approximately 3 kg/cm ² ·G, the pressure is slightly insufficient to solve the above problem. In the method of using a hot press, it is more preferable to cover the coating film with a plastic film such as a polyester film or a Teflon film and then heat press it, since a mirror surface can be imparted to the coating film surface. (Effects of the Invention) Since the present invention is a method for producing such painted formwork plywood, the paint used is less expensive than conventional acrylic paints or urethane paints, and can be cured by heating. The time can be reduced significantly, and productivity can also be greatly improved. In addition, as for the number of times the paint is applied, whereas conventional acrylic paints and urethane paints require two to three times, the present invention allows a coating film of an appropriate thickness to be obtained in just one time. Furthermore, as can be seen from the Examples and Comparative Examples, the performance of the coating film is superior to that obtained using conventional acrylic paints. Furthermore, the present invention can reduce the amount of paint applied to the formwork plywood compared to the method disclosed in Japanese Patent Application No. 60-283841, which was previously filed by the present inventors, so it is economically advantageous in this respect as well. It is. In addition, in the present invention, since the heat-pressing curing method can be used to heat-cure the paint, it is now possible to use low-grade logs that could not previously be used as formwork plywood surface materials because of their tendency to warp. In this respect as well, significant cost reductions can be achieved. As described above, the coated form plywood obtained by the method of the present invention can use cheaper raw materials than conventional ones. Its effects are extremely significant, such as higher production efficiency and better performance than those using acrylic paint. (Examples and Comparative Examples) The present invention will be specifically explained below using Examples and Comparative Examples. Example 1 Carboxy-modified styrene-butadiene synthetic rubber latex (43% butadiene, 51% styrene, 6% acrylic acid, 48% solids) was added to 60 parts of urea resin (molar ratio of formaldehyde and urea: 1.8) with a solid content of 70%. 40 parts, silicone modifier (Shin-Etsu Chemical Co., Ltd.)
A coating composition was prepared by adding 0.2 parts of Shin-Etsu Silicone KF351 (manufactured by Shin-Etsu Silicone KF351) and 30 parts of talc (Three S, manufactured by Nippon Talc Co., Ltd.) as a filler. This coating composition is further mixed with a white pigment (OR-650 manufactured by Resino Color Industries Co., Ltd.) and a black pigment (LN-750 manufactured by Resino Color Industries Co., Ltd.) to form a gray pigment, and 5 parts, and a curing accelerator. Add 1 part of ammonium chloride as 220g/m ² on one side of the formwork plywood using a natural coater and reverse coater.
It was applied at the rate of The form plywood coated with the coating composition was then placed in a dryer and pre-dried for 10 minutes at a temperature of 60°C. After pre-drying, the entire surface of the formwork plywood was covered with a 100 μm thick unsaturated polyester film (Mylar film manufactured by DuPont, USA).
Using a hot press at a temperature of 120℃ and a pressure of 10Kg/
The coated formwork plywood was manufactured by hot pressing for 120 seconds under the conditions of cm ² G. The physical properties of the obtained painted formwork plywood are as shown in Table-1. Example 2 N-methylol-modified styrene-butadiene synthetic rubber latex (butadiene 45%, styrene 52%, N-methylol acrylamide 3%, solid content 48%), 2 parts of polyethylene wax, and 50 parts of clay (manufactured by Nippon Bentonite Co., Ltd.) as a filler were added to prepare a coating composition. To this coating composition, 5 parts of a pigment (same as in Example 1) and 1 part of ammonium chloride as a hardening accelerator were added to a mold made of erima wood (a material that easily warps). on both sides of the plywood,
It was applied at a rate of 170 g/m ² using a knife coater. The form plywood coated with the coating composition was placed in a dryer and pre-dried for 15 minutes at a temperature of 50°C. Immediately after pre-drying, the entire surface of the formwork plywood was covered with an unsaturated polyester film (Lumirror, manufactured by Toray Industries, Inc.) with a thickness of 188 μm, and then heated at a temperature of 110°C and a pressure of 15 kg/cm as in Example 1. cm ²・G condition 60
A coated formwork plywood with a smooth surface was produced by heat pressing for seconds. The physical properties of the obtained painted formwork plywood are as shown in Table-1. Example 3 A glycidyl-modified styrene-butadiene synthetic rubber latex (butadiene 45%, styrene 52%, glycidyl methacrylate 3%, solids content 48%) and 2 parts of the same modifier used in Example 1 and the same talc used in Example 1 as filler.
40 parts were added to form a coating composition. To this coating composition, 4 parts of the same pigment as used in Example 1 and 1 part of ammonium chloride as a curing accelerator were added to only one side of the formwork plywood at a rate of 270 g/m ² . It was coated with The form plywood coated with the coating composition was then placed in a dryer and pre-dried for 8 minutes at a temperature of 70°C. After pre-drying, formwork plywood is 250μm thick.
Using an endless heater roll made of unsaturated polyester sheet, roll and harden it at a temperature of 130℃ for 10 seconds, then put it in the dryer again and dry it for 10 minutes at 120℃ to form the painted formwork plywood. Manufactured. The physical properties of the obtained painted formwork plywood are as shown in Table-1. Comparative Example 1 Various physical properties of painted formwork plywood using a commercially available acrylic paint were measured. Table the results.
Shown in 1. As shown in Table 1 in the Examples and Comparative Examples above, the painted form plywood obtained by the present invention had better physical properties than the painted form plywood using conventionally known acrylic paints. . Comparative Example 2 Carboxy-modified styrene-butadiene synthetic rubber latex (43% butadiene, 51% styrene, 6% acrylic acid, 48% solids) was added to 60 parts of urea resin (molar ratio of formaldehyde and urea: 1.8) with a solid content of 70%. 40 parts, silicone modifier (Shin-Etsu Chemical Co., Ltd.)
0.2 part of Shin-Etsu Silicone KF351) was added to prepare a paint composition. To this coating composition, 5 parts of pigment (same as in Example 1) and 1 part of ammonium chloride as a hardening accelerator were added, and a coating of 150 g/m ² was applied to only one side of the form plywood using a natural coater and a reverse coater.
It was applied at the rate of The form plywood coated with the coating composition was then placed in a dryer and pre-dried for 10 minutes at a temperature of 60°C. However, the coating form plywood after pre-drying had a problem with a thin coating film, so the above coating composition was not used.
After coating again at 100 g/m ² , preliminary drying was performed under the same conditions as above. The pre-dried formwork plywood was covered with a 100 μm thick unsaturated polyester film (Mylar film manufactured by DuPont, USA) over the entire surface of the coating, and then heated using a hot press at a temperature of 120°C and pressure.
The coated formwork plywood was manufactured by hot pressing for 120 seconds under the conditions of 10Kg/cm ² ·G. The physical properties of the obtained painted formwork plywood were good as shown in Table 1. The various tests were conducted using the following methods. 1 Slag adhesion test Pour concrete with the composition shown in the table below into the formwork.
Cured at 20℃ for 2 days. After curing, remove the formwork and observe the state of peeling. Repeat this operation 10 times. (Observation items) (1) Degree of slag adhesion (condition of adhesion of concrete to paint film) (2) Ease of peeling (ease of peeling of formwork plywood from concrete)

[Table] 2 Water resistant adhesion test A grid grid of 2 mm intervals is drawn on the coating surface, and this is 100
A test piece cut into squares (10 squares each vertically and horizontally)
After 48 hours of immersion in water, the water on the paint surface is thoroughly wiped off, and after pasting packing tape on the coating surface, this is peeled off and the surfaces of the coating film and packing tape are observed. 3 Blocking property test The coated and non-coated sides of a test piece cut into 30 cm squares were placed one on top of the other, and a load of 20 kg was applied to the test piece at 20°C.
After leaving it for 48 hours, remove the load and observe whether there is any blocking on the coating surface. 4 Cold and heat cyclic test (B test) According to the JAS special plywood test method. 5 Plane tensile test According to JAS special plywood test method. 6 Alkali resistance test Compliant with JAS special plywood test method. (20% sodium hydroxide aqueous solution was used instead of 1% sodium carbonate aqueous solution.) 7 Acid resistance test Compliant with JAS special plywood test method. (Use 10% formic acid aqueous solution instead of 5% acetic acid aqueous solution.)

【table】

Claims (1)

[Claims] 1. A compound having a conjugated diene bond (first component), a vinyl monomer (second component), and a carboxyl group,
From a copolymer with a reactive monomer (third component) having a crosslinkable reactive group in its side chain selected from the group consisting of N-methylol group, glycidyl group, hydroxyl group, amino group, amide group, and acid anhydride. Production of coated form plywood, characterized in that a composition consisting of a modified synthetic rubber latex, a heat-curable amino resin, a filler, and a modifier is applied to one or both sides of form plywood, and then heated and cured. Method. 2. The method for producing painted formwork plywood according to claim 1, wherein the compound having a conjugated diene bond is butadiene or isoprene. 3 The ratio of the first component to the second component is 20 to 80% by weight of the first component relative to the total amount thereof, and the ratio of the third component is 0.1 to the total amount of the first component and the second component.
~20% by weight in claim 1 or 2
Method for manufacturing painted formwork plywood as described in Section 1. 4. The method for producing coated formwork plywood according to claim 1, 2, or 3, wherein the heat-curable amino resin is a urea resin, a melamine resin, or any one of these co-condensed resins. 5. The method for producing painted formwork plywood according to claim 4, wherein the solid content concentration in the heat-curable amino resin is 60% by weight or more. 6. Claim 1, wherein the ratio of the modified synthetic rubber latex to the heat-curable amino resin is 50 to 400 parts by weight relative to 100 parts by weight of the solid content in the modified synthetic rubber latex.
The method for producing painted formwork plywood according to item 1 selected from items 1 to 5. 7. Claims 1 to 6, wherein the proportion of the modifier is 0.2 to 10% by weight based on 100 parts by weight of the total solid content in the synthetic rubber latex and solid content in the heat-curable amino resin. A method for manufacturing painted formwork plywood according to item 1 selected from. 8. Claims 1 to 7, wherein the proportion of the filler is 20 to 200 parts by weight based on 100 parts by weight of the total solid content in the modified synthetic rubber latex and solid content in the heat-curable amino resin. A method for manufacturing painted formwork plywood according to item 1 selected from.