JPH0574434B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a novel method for 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-quality 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) In addition, acrylic paints and urethane paints contain organic solvents, and since these organic solvents are released during the drying process, equipment for recovering the volatilized organic solvents is required as a pollution control measure. (4) Acrylic paints and urethane paints belong to the class of expensive paints, so using such paints on painted plywood, which is consumed in large quantities, poses a cost problem. (Means for Solving the Problems) The inventors of the present invention have solved these problems, and as a result of intensive studies on manufacturing coated formwork plywood with good workability and productivity, and at low cost. The inventors have discovered that this problem can be solved by using a paint consisting of a modified synthetic rubber latex, a heat-curable amino resin, and a modifier, and have thus arrived at 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 having a crosslinkable reactive group selected from the group consisting of an amide group and an acid anhydride (third component)
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 and a modifier (hereinafter referred to as the coating composition) is applied to one or both sides of the formwork plywood, and then heated and cured. It is characterized by: (Specific Means for Carrying Out the Invention) The present invention will be explained in detail. The modified rubber latex used in the present invention can be produced by the same method as the modified synthetic rubber latex used in the invention described in JP-A No. 62-27107, which was previously filed by the present inventors. 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 deformed synthetic rubber latte 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 paint film of the painted form plywood manufactured using the latex will become too hard and cracks will easily occur on the paint film surface, while if it exceeds 80%, the painted mold This is not desirable because the painted surface of the frame 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-methylolmethacrylamino, 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 acrylic 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. This is a term used to indicate that the cloudy part reduces the acid and alkali resistance of the coating film.) 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%. In the present invention, this commercially available product can be used as it is. Next, the heat-curable amino resin (hereinafter simply referred to as amino resin) used in the present invention is as follows:
Examples include urea resins, melamine resins, 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. Moreover, 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 a plywood form, a coating film with an appropriate thickness is obtained. 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 process of heating and curing the coating composition, local curing failure, commonly known as clouding, will likely occur, and the alkali resistance and mortar resistance of that area will decrease. On the contrary, 80%
Amino resins with solid content concentrations above are difficult to manufacture and 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 acid and chemical resistance of the coating will also deteriorate, resulting in a coating that is not strong enough to withstand concrete mortar. This is not preferable because membrane performance cannot be obtained. Examples of the modifier used in the present invention include polyoxyethylene noniphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene oleyl ether, Oxyethylene lauryl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether,
Ethers such as polyoxyethylene lanolin alcohol ether and polyoxyalkylamine ether, esters such as polyoxyethylene distearate and polyoxyethylene lanophosphate, fatty acid diethanolamides, or sulfonated or phosphate compounds of these compounds, Silicone compounds such as dimethylpolysiloxane silicone, methyl silicone, dimethyl silicone, methylhydrogen polysiloxane silicone, methyl phenyl silicone, fluorosilicone, and compounds in which the methyl group of dimethyl polysiloxane is converted into α-methylstyrene, α-olefin compounds, polyetherified compounds, trifluoroalkylated compounds, amidated compounds, mercaptolated compounds, epoxidized compounds, carboxylated compounds, or polyolefin wax emulsions such as polyethylene waxes and polypropylene waxes. etc., and one or more of these compounds can be used. The amount of the modifier added is preferably 0.2 to 10% based on the total amount of solid content in the synthetic rubber latex and solid content in the amino resin. If it is less than 0.2%, 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%, 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. In the present invention, a coating composition is prepared by mixing a modified synthetic rubber latex, an amino resin, and a modifier at room temperature, and the mixing order of the three components is as follows. That is, after mixing the modified synthetic rubber latex and the amino resin, the modifier is added thereto, but it is also possible to mix either the modified synthetic rubber latex or the amino resin and the modifier beforehand and then mix the two. . 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. Although the amount of the pigment added varies depending on the hue of the pigment, it is generally appropriate to add the pigment in an amount of 1 to 5% based on the coating composition. To the thus obtained coating composition, a conventionally known curing accelerator for amino resins (hereinafter simply referred to as curing accelerator) such as ammonium chloride, ammonium sulfate, ammonium nitrate, etc. is added in an amount of 1 to 3% based on the amino resin. It is preferable to do so. 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 100 to 500 g/m ² per surface area of the form plywood, preferably
It is 200-400g/ ^m2 . If the coating amount is less than 100g/ ^m2 , a sufficiently thick coating layer will not be formed;
If it is more than g/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 a 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 coating composition is applied to the formwork plywood and then suddenly hot-pressed, the paint composition still has fluidity, so it flows out of the formwork plywood, resulting in an underapplication, resulting in a uniform and continuous coating. However, it is not possible to obtain a coating film with a suitable thickness, and furthermore, it is not possible to obtain a coating film with 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. If pre-drying is performed, the surface of the coating composition applied to the form plywood will be formed, and the viscosity of the coating composition will also increase significantly, so the above problem will not occur during hot pressing, and the coating film of appropriate thickness will be formed. It is possible to obtain. 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.
Conducted 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. In the present invention, painted form plywood can be obtained in this way, but the thickness of the coating may be insufficient in one application of the coating composition, so in this case, the coated form plywood obtained By applying the coating composition once again and heating and curing it again, a coating film with an appropriate thickness can be obtained. (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 it can be heated to cure easily. 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 almost 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. In addition, in the present invention, the heat-pressing curing method can be used to heat-cure the paint, so 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 mentioned above, the painted form plywood obtained by the method of the present invention can use cheaper raw materials than conventional ones, has high production efficiency, and has better performance than those using acrylic paint. , its economic hardening is extremely large. (Examples and Comparative Examples) The present invention will be specifically explained below using Examples and Comparative Examples. Example 1 60 parts of a urea resin with a solid content of 70% (molar ratio of formaldehyde and urea 1.8) was mixed with carboxy-modified styrene-butadiene synthetic rubber latex (43% butadiene, 51% styrene, 6% acrylic acid, solid content (48%)). ) and 0.2 parts of a silicone modifier (Shin-Etsu Silicone KF351, manufactured by Shin-Etsu Chemical Co., Ltd.) to prepare a coating composition. To this coating composition, a white pigment (OR-650, manufactured by Resino Color Industries, Ltd.) was added. ) and black pigment (LN-750 manufactured by Resino Color Industries Co., Ltd.) to form a gray pigment, 5 parts, and 1 part of ammonium chloride as a hardening accelerator were applied to only one side of the formwork plywood using a natural coater and a reverse coater. The formwork plywood coated with the coating composition was then placed in a dryer and pre ^- dried for 10 minutes at a temperature of 60°C.The mold after pre-drying After covering the entire surface of the frame plywood 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%) and 2 parts of polyethylene wax 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 200 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%, solid content 48%) and 2 parts of the same modifier as used in Example 1 were added to prepare 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 hardening accelerator were added to only one side of the formwork plywood at a rate of 300 g/m ² . It was coated with The form plywood coated with the coating composition was then placed in a dryer and pre-dried at a temperature of 70°C for 8 minutes. After pre-drying, the formwork plywood has a thickness of 250 μm.
Using an endless heater roll made of unsaturated polyester sheet, roll and harden it at 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. . 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 and cure at 20℃ for 2 days. After curing, remove the formwork and observe the state of peeling. This operation
Repeat 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 resistance adhesion test Make base marks at 2 mm intervals on the coating surface and
A test piece cut into 100 squares (10 squares each vertically and horizontally) was immersed in water for 48 hours, the water on the paint surface was thoroughly wiped off, and duct tape was pasted on the painted surface, which was then peeled off. Observe the coating surface and the surface of the duct tape. (3) Blocking property test The coated and non-coated surfaces of test pieces cut into 30 cm squares were placed one on top of the other, and a load of 20 kg was applied to the test pieces at 20°C.
After 48 hours, the load was removed and the presence or absence of blocking on the coating surface was observed. (4) Cold and heat cyclic test (B test) Based on the JAS special plywood test method. (5) Planar tensile test According to JAS special plywood test method. (6) Alkali resistance test Compliant with JAS special plywood test method. (1%
Use 20% sodium hydroxide aqueous solution instead of sodium carbonate aqueous solution. ) (7) Acid resistance test Compliant with JAS special plywood test method. (5%
Use 10% formic acid aqueous solution instead of acetic acid aqueous solution. )

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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. A method for producing coated formwork plywood, which comprises applying a composition comprising a modified synthetic rubber latex, a heat-curable amino resin, and a modifier to one or both sides of formwork plywood, and then heating and curing the composition. 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 80% by weight relative to the total amount of the first component and the second component.
20% by weight of the method for producing painted formwork plywood according to claim 1 or 2. 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 No. 6, wherein the ratio of the modified synthetic rubber latex to the heat-curable amino resin is 50 to 400 parts by weight based on 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, 2, 3, 4, or 5. 7. Claims 1 and 2, wherein the proportion of the modifier is 0.2 to 10% by weight based on the total amount of solid content in the synthetic rubber latex and solid content in the heat-curable amino resin. The method for producing painted formwork plywood according to item 3, 4, 5, or 6.