JPS6146289B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a strong and smooth polyolefin resin coating on the surface of plywood used as concrete formwork.

The surface of concrete formwork plates is required to have impact resistance and durability as well as releasability from the concrete surface due to the harsh conditions of use.

In order to meet such demands, the present inventor has devised a method for forming a polyolefin resin film on the surface of plywood, which uses powdered resin to avoid damage caused by water vapor generated from wood, and which can also be applied to wood in a short period of time. We have developed a method for thermal fusion, and at the same time invented a method for manufacturing inexpensive concrete formwork plates that improves surface strength and mold releasability.

Next, the method of the present invention will be explained.

The drawing is a schematic diagram of an apparatus for carrying out the method of the invention. First, a powder 2 of polyolefin copolymer resin (hereinafter referred to as adhesive resin) having adhesive properties is applied to the surface of the plywood 1 through a powder spreader 3 while conveying the plywood 1 for concrete formwork by the roller conveyor 12. Adhesive resin powder to be sprayed at a rate of 20g/ ^M2 is, for example, a graft polymerization of an acid anhydride such as maleic anhydride based on a polyolefin, such as Admar, NS-100 manufactured by Mitsui Petrochemical Industries, Ltd. Use a material that has been added with adhesive properties. There is no problem with the particle size of the powder as long as it is under 30 mesh. The powder spreader 3 may be any device that can evenly drop a certain amount of powder, but it is even better to use an electrostatic powder coating machine.

Next, the plywood surface is preheated together with the powder by passing it under a heating device 4 such as infrared rays, and then heated and pressurized by passing it through a heating roll 5 to firmly bond the adhesive resin and the plywood and to reduce the unevenness of the plywood surface as much as possible. The pressure of the roll 5 is maintained at a linear pressure of 20 kg/cm or more, and the adhesive resin coating is performed while pressing down the convex portions on the surface. At this time, the adhesive resin layer does not become a complete film, but remains porous and does not impede gas flow.

Subsequently, powder 6 of a non-adhesive polyolefin resin (hereinafter simply referred to as polyolefin resin) is sprinkled onto the surface of the adhesive resin layer through a second powder spreader 7. The amount of spraying can be adjusted as appropriate depending on the durability requirements of the product, but the appropriate amount is 50 to 150g/ ^M2.As the polyolefin resin, it is best to use the same type of adhesive resin as the adhesive resin used for the adhesive layer. For example, when an adhesive resin based on polyethylene resin with added adhesive properties is used for the adhesive layer, it is desirable to use polyethylene resin as the polyolefin resin.

In addition, the particle size is preferably 50 to 200 mesh, and the grade is preferably one with as large a molecular weight as possible. Then,
The resin powder is heated through a second heating device 8 and passed through a second heating roll 9 to be heated and pressurized to form a surface resin layer. The average thickness of the surface resin layer is 50~
150 microns and forms a complete film. Second
If the heating device 8 is used to sufficiently heat the film, even one second heating roll 9 can form a complete coating. Once the resin surface has formed a film, it is desirable to cool it as quickly as possible.

Therefore, after passing through the second heating roll 9,
Immediately pass the cooling roll group 10 through the cooling air device 1
From step 3, blow low-temperature air to rapidly cool the resin surface. In this case, the surface temperature of the cooling roll group 10 is 10
A temperature between .degree. C. and 25.degree. C. is suitable, and the temperature of the air blown from the cooling air device 13 must be lower than this temperature in order to maintain the surface temperature of the cooling roll group 10 at the above temperature. The resin surface that is rapidly cooled in this manner has smaller crystals and a smoother surface, which improves both the durability and mold releasability of the product.

Furthermore, although a large amount of water vapor is generated from the plywood as it is heated by the second heating device 8, the amount of adhesive resin passes freely due to its porous nature, and the polyolefin resin sprayed on the top surface of the plywood Since the resin is also a powder, the generated water vapor evaporates freely, causing no damage, and the vapor pressure inside the plywood does not increase. However, after the resin surface has formed a complete coating through the second heating roll 9, the degassing port for the water vapor generated from the plywood is blocked, and the vapor pressure increases, pushing up the resin coating from below and creating bubbles. begins to occur. The time for bubbles to appear varies depending on the melt index of the resin, but usually starts from 1.5 to 5 seconds after passing through the second heating roll and is 10 to 40 seconds.
The peak occurs after a few seconds. Therefore, in order to suppress the generation of bubbles, the resin temperature should be immediately lowered to 80°C after the film is formed.
It is necessary to cool it below ℃. For example, the heat deformation temperature of high-density polyethylene resin used as a surface material is 80°C to 93°C, so if the resin is cooled to 80°C or lower, there is no fear of bubble generation.

As mentioned above, in order to avoid problems caused by water vapor until just before the coating is formed with the second heating roll, it is necessary to use resin powder, and after the coating is formed, the resin surface is quickly cooled and the surface A feature of the method of the present invention is that the performance of the product is improved by reducing the size of resin crystals.

As a rapid cooling method, it is preferable to provide the cooling roll group 10 as close as possible to the second heating roll 9 and circulate cold water inside each cooling roll group, but at the same time, use a cold air device 13 or cold water spray. A device 11 is used to blow cold air or cold water. In addition,
By operating the cold air device 13 and the cold water spray device 11 at the same time and spraying cold air and cold water onto the resin surface, the cooling rate of the resin is further accelerated, crystals are further reduced, and the surface properties of the product are improved. becomes.

The concrete formwork board manufactured by the method of the present invention has a polyolefin resin layer on the surface,
Shows excellent durability and mold releasability. When producing this on an industrial scale, increasing the capacity of the heating device can increase the production speed proportionally.
In addition, raw resin can be replenished simply by feeding it into the hopper, allowing continuous production at high speed. Furthermore, since the raw material resin powder is relatively inexpensive, high-quality concrete formwork plates can be supplied in large quantities at low cost.

Next, the present invention will be explained by examples.

<Example 1> Using the device shown in the drawings, the heating roll 5 and the second heating roll 9 were set at 220°C, the cooling roll group 10 circulated cold water at 150°C, and the heating device 4 and the second heating roll 9 were set at 220°C. As the heating device 8 of No. 2, an infrared heating furnace with a length of 4 m is used.
The second powder spreader 7 was an electrostatic powder coating machine, the cold air device 13 was a Colder low-temperature air generator based on the principle of a vortex tube, and the conveyor conveyor 12 had a feeding speed of 10 m/min. As adhesive resin powder 2, Admar, NS-100, manufactured by Mitsui Petrochemical Industries, Ltd., 50-150 mesh powder was used, and as polyolefin resin powder 6, Hi-Zex, 8200CP, manufactured by Mitsui Petrochemical Industries, Ltd. (50 to 200 mesh) was used. The plywood used was a commercially available 5-ply plywood with a thickness of 12 mm.

On top of the plywood 1, apply the adhesive resin powder 2 for 20 minutes.
After passing through the heating device 4 and heating roll 5 while uniformly scattering at a ratio of 120 g/M ² , the polyolefin resin powder 6 is spread at a ratio of 120 g/M ² , and then a second Immediately after passing through the heating device 8 and the second heating roll 9, the cooling roll group 1
0, and while blowing cold air at 5° C. using the cold air device 13, rapid cooling was performed by the cooling roll group without operating the cold water spray device 11.

At this time, the distance between the second heating roll 9 and the first roll of the cooling roll group was 400 mm, and the travel time was 2.4 seconds. In this way, a plywood for concrete formwork with excellent durability and mold releasability was obtained.

<Example 2> The same equipment as in Example 1 is used, and the steps from the powder spreader 3 to the second heating roll 9 are performed in the same manner as in Example 1. When cold water was sprayed onto the resin surface in the form of a mist using the cold water spray device 11 installed immediately after the first roll in the roll group, the water droplets adhering to the resin surface were removed while passing through the cooling roll group. Most of it evaporated, and the surface temperature at the end of the cooling roll group was found to be lower by an average of 7°C compared to Example 1. The thus obtained plywood for concrete formwork had very small crystals on the resin surface, and a clear improvement was seen in durability and mold releasability.

<Example 3> The same equipment as in Example 1 is used, and the same method as in Example 1 is used from the powder spreader 3 to the second heating roll 9, and when passing through the cooling roll group 10, cooling When the cold water spray device 11 installed immediately after the first roll in the roll group was used to spray cold water in the form of a mist onto the resin surface, the cold air device 13 was used to blow cold air at the same time. Most of the water droplets adhering to the cooling rolls evaporated while passing through the cooling roll group, and the surface temperature at the end of the cooling roll group was found to be lower by an average of 3°C compared to the case of Example 2.

The thus obtained plywood for concrete formwork has very small crystals on the resin surface, and has excellent durability and mold releasability.

[Brief explanation of the drawing]

The drawing is a schematic illustration of an embodiment of a device for carrying out the method of the invention. 1...Plywood, 2...Adhesive polyolefin copolymer resin powder, 3...Powder spreader, 4
...Heating device, 5...Heating roll, 6...Non-adhesive polyolefin resin powder, 7...Second powder spreader, 8...Second heating device, 9...Second heating roll , 10... Cooling roll group, 11... Cold water spray device, 12... Roll conveyor, 13... Cold air device.

Claims (1)

[Claims] 1 Spread adhesive polyolefin copolymer resin powder on the surface of the plywood, preheat it, then heat and pressurize it with a heated roll to melt the resin powder and heat-seal it to the plywood surface, forming the plywood. A breathable adhesive layer made of adhesive polyolefin resin is formed on the surface, and then powder of the same type of non-adhesive polyolefin resin is sprinkled on the surface, which is preheated and then heated again with a heating roll. After applying pressure to form a non-adhesive polyolefin resin layer on the surface, when passing through the cooling roll group, the resin layer is rapidly cooled from the surface by blowing cold air and/or cold water, and the resin temperature is 80°C. A method for manufacturing concrete formwork plates characterized by rapid cooling to below ℃.