JPS62117954A - Production of plywood for concrete mold frame - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing plywood for concrete formwork, which is excellent in economy, weather resistance, durability, on-site workability, and finish quality on cement surfaces.

[Conventional technology and problems] Although conventional plywood for concrete formwork is inexpensive, it suffers from contamination of the finished concrete surface due to extracted components of the plywood, poor concrete hardening, and lacks aesthetic appeal on the finished surface, as well as poor durability. It had disadvantages inferior to that of As a measure to eliminate this drawback, a method has been taken in which a polyolefin sheet is attached to plywood. Although improvements were made by this method, there were problems in that the adhesive strength between the plywood and the sheet tended to vary and the durability became unstable. Furthermore, in order to improve these drawbacks, the former method involves improving the adhesion between plywood and polyolefin sheets using expensive adhesives such as epoxy resin-modified acrylic resin adhesives, and furthermore, using adhesive polyolefin copolymerization methods. (A method in which a bed of fat powder is spread, heated and pressurized, and then non-adhesive polyolefin copolymer resin powder is spread, heated and pressurized, and then cooled and molded.)
JP-A-6O-151004), and in the latter case, a method for improving durability by improving mold releasability from concrete (JP-A-6O-903) is known.

However, both methods use expensive special resins such as adhesive polyolefin copolymer resins, epoxy resin-modified acrylic resin adhesives, and fluorine-containing polymers, making them less economical and less durable. There was a problem that the product was not fully satisfactory.

[Means for solving the problem] As a result of intensive research to obtain an ideal plywood for formwork that is inexpensive, has excellent weather resistance, durability, on-site workability, and cement finishability, the present inventors have developed a plywood for concrete formwork. By applying ethylene vinyl acetate copolymer resin to the plywood and then covering it with thermoplastic synthetic resin, which has a higher surface hardness than ethylene vinyl acetate copolymer resin, the adhesive strength and weather resistance between the synthetic resin and the plywood are improved, making it ideal. The present invention was achieved by discovering that plywood for formwork can be made.

Originally, plywood for concrete formwork is resistant to external factors such as the effects of rain, wind, ultraviolet rays, etc. when used outdoors, leaching of alkaline water related to concrete hydration reactions, and temperature increases on the board surface due to exothermic reactions. Therefore, plywood is required to be classified as a class according to the Japanese Agricultural Standards, and the synthetic resin coated on the plywood must have performance equivalent to or better than that of plywood. For that reason,
The coating synthetic resin is bonded using the above-mentioned epoxy resin-modified acrylic resin, adhesive polyolefin copolymer resin (with the addition of maleic anhydride, etc., it corresponds to type 1) as an adhesive, but it is expensive and The adhesive itself is hard and does not easily peel off, and the internal stress generated from the difference in expansion and contraction caused by external factors between the resin and the plywood cannot be sufficiently alleviated, and the resin layer tends to crack. In order to eliminate these drawbacks, the resin of the adhesive layer should exhibit the stress-relieving function of the RM resin and the plywood, and it should also be possible to form a layer that complies with the Japanese Agricultural Standards. It has been discovered that in order to satisfy this requirement, it is sufficient to apply an ethylene vinyl acetate copolymer resin to the plywood under certain conditions and cover it with a synthetic resin. In other words, the ethylene-vinyl acetate copolymer resin coated on the plywood impregnates and strengthens the surface layer of the plywood, so that the resin anchoring is performed more firmly, increasing the adhesive strength between the plywood and the covering synthetic resin. Cracks that occur in the synthetic resin coating occur because the expansion and contraction rate of plywood is greater than that of the synthetic resin, and impregnation of the plywood surface layer with resin by this method suppresses the expansion and contraction of the plywood due to external factors, so the synthetic resin This is an effective means of preventing cracks from forming. Furthermore, ethylene vinyl acetate copolymer resin has the highest elongation rate among synthetic resins and has a low tensile modulus, so it also acts as a stress reliever for the plywood and the coating synthetic resin. . It also has the advantage of being inexpensive. Of particular note is the discovery that since the adhesive is bonded by the anchoring effect of the coating synthetic resin, even ethylene vinyl acetate copolymer resin, which normally does not have the same adhesive strength, is sufficiently stable and can be put to practical use. It is.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below based on the drawings. Figure 1 is a sectional view of the plywood for concrete formwork of the present invention, in which a solution of ethylene vinyl acetate copolymer resin 2 is applied to the plywood 3, and a solution of ethylene vinyl acetate copolymer resin 2 is applied on the plywood 3.
It is coated with a thermoplastic synthetic resin 1 having higher surface hardness. The ethylene-vinyl acetate copolymer resin used in the present invention preferably has a vinyl acetate resin content of 7% to 50% by weight, particularly one having a content of 20% to 40% by weight. If the vinyl acetate resin content is within the above range, the flexibility of the ethylene-vinyl acetate copolymer resin will be appropriate, and the effect of stress relaxation against expansion and contraction between the plywood and the covering synthetic resin will be exerted, thereby preventing the occurrence of cracks in the covering synthetic resin. It can be suppressed. In other words, it improves the weather resistance and durability of the product. When the vinyl acetate content is less than 7% by weight, the plywood lacks flexibility and cannot be expected to be effective in suppressing cracks in the coating synthetic resin that occur due to the difference in expansion and contraction between the plywood and the coating synthetic resin. On the other hand, when the temperature exceeds 50 times, a decrease in heat-resistant adhesion is observed, probably due to the influence of the properties of the vinyl acetate resin. In addition, ethylene vinyl acetate copolymer resin can be treated with IflI solvent such as benzene or toluene.
Dilute from twice the amount to 10 times the amount (weight ratio) and roll coater.
It is applied with a coating machine such as
．． 5g/m2 to 10g/112, especially 1g/f
The most desirable one is f12 to 5 g/m2. When the coating amount is less than 0.5 g/m'', no adhesive effect is exhibited, and on the other hand, when it exceeds 10 g/m2, a decrease in heat-resistant adhesion is observed.

Furthermore, after applying the ethylene vinyl acetate copolymer resin, a thermoplastic synthetic resin having a higher surface hardness than the ethylene vinyl acetate copolymer resin was applied using a T-die from 0.1211Ifi+ to 0.3.
The extrusion coating is applied to a thickness of mm, and the two are heat-sealed and then cold-pressed.

The thermoplastic synthetic resins used (51 resins include polyethylene resin, polypropylene resin, polyvinyl chloride 454 resin, etc.), but from the viewpoint of durability, they have high surface hardness, weather resistance,
High-density polyethylene resin is preferred because it is economical and has excellent adhesiveness to ethylene-vinyl acetate copolymer resin.

If the resin thickness is within the above range, the adhesive strength with plywood,
Good weather resistance and durability. Resin thickness is 0.12m
If it is less than +a, the thickness of the synthetic resin is so thin that unevenness, cracks, etc. on the plywood surface are likely to be exposed on the product surface, and weather resistance and durability are also poor. On the other hand, when the resin thickness exceeds 0.3 mm, it has the disadvantage of being inferior in economic efficiency.

In addition, the coating synthetic resin can be supplied by a resin powder scattering method or a T-die extrusion method, but the former method tends to cause uneven distribution of the powder due to its mechanism, making it difficult to accurately measure the thickness of the synthetic resin, making it difficult to achieve weather resistance and durability. In order to use it as plywood for concrete formwork, it is necessary to set a large average film thickness, which has the disadvantage of poor stability and economy. On the other hand, since the T-die allows the synthetic resin film thickness to be distributed relatively uniformly, it is possible to supply products with excellent stability and economic efficiency.

Note that it is desirable that the plywood to be subjected to this method has a low moisture content in advance. When this comes into contact with the high-temperature coating synthetic resin supplied from the T-die, the moisture contained inside the plywood evaporates or the air body M4 expands to prevent blistering defects on the surface of the product by pushing up the fat layer. Specifically, plywood is dried by infrared irradiation to reduce its moisture content.

Colorants, ultraviolet absorbers, stabilizers, etc. can be added to this synthetic resin as appropriate.

[Effects of the Invention] As stated above, the plywood for concrete formwork of the present invention has an ethylene-vinyl acetate copolymer resin coated between the plywood and the coating synthetic resin for the purpose of stress relaxation and reinforcement of adhesion. Because of this, it has superior weather resistance and durability compared to conventional products, and has the advantage of being able to be used repeatedly. Furthermore, since this product does not require any special resin, it is possible to obtain plywood for concrete formwork that is highly economical.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a plywood for concrete formwork showing one embodiment of the present invention. 1... Thermoplastic synthetic resin 2... Ethylene vinyl acetate copolymer resin 3... Plywood

Claims (1)

[Claims] A method for manufacturing plywood for concrete formwork, which comprises applying an ethylene vinyl acetate copolymer resin to the surface of the plywood, and then covering the plywood with a thermoplastic synthetic resin having a surface hardness higher than that of the ethylene vinyl acetate copolymer resin.