GB2092063A - Coated board for concrete form and method of making the same - Google Patents

Abstract

A coated board for concrete forms comprises a wooden substrate such as plywood, fiberboard, particle board or veneer with a layer of adhesive thermoplastic copolymer adhered thereon by heat and pressure. The copolymer is an acrylate modified polyethylene or polypropylene copolymer or a copolymer of ethylene with vinylacetate or ethylacrylate. A method of making this coated board comprises applying the copolymer to the substrate, covering this layer with a release film or other sheet of thermoplastic material having a higher melting point than that of the copolymer, applying heat and pressure to melt the copolymer but not the release film or outer sheet, and allowing the melted thermoplastic copolymer to solidify slowly without exposure to ambient air.

Description

SPECIFICATION Coated board for concrete form and method of making the same A coated board for concrete forms is disclosed. The coated board comprises a wooden substrate such as plywood, fiberboard, particle board, veneer, and the like and a layer of high adhesive thermoplastic copolymer adhered theron by the application of heat and pressure. Said high adhesive thermostatic copolymer is selected from the group consisting of acrylate denatured polyethylene copolymer, acrylate denatured polypropylene copolymer, ethylene vinylacetate copolymer, and ethylene ethylacrylate copolymer, and will exert higher adhesive strength when welded onto the surface of the wooden substrate. A method of making this coated board is also disclosed herein.The method comprises applying a high adhesive thermoplastic copolymer on an upper surface of the wooden substrate, covering this layer of copolymer with a release film or outer sheet of thermoplastic material having a higher melting point than that of the copolymer to sandwich the layer of the copolymer between the wooden substrate and the release film or outer sheet, applying heat and pressure to the sandwich thus formed to melt the thermoplastic copolymer while leaving the release film or outer sheet unmelted, and leaving this sandwich so as to allow the melted thermoplastic copolymer to solidify slowly without being exposed to the ambient air so that the thermoplastic copolymer welds firmly in the surface of the substrate.

This invention relates to a coated board for concrete form, particularly to a coated board used for concrete form of a wooden substrate and a layer of thermoplastic copolymer adhered thereon, and a method of making the same.

There have been employed largely wooden boards as concrete form boards in the fields of civil engineering and construction works.

Such wooden boards includes cellulosic materials such as plywood, particle board, and fiberboard. However, these materials will cling to a finished concrete during the curing of the concrete since fresh concrete will penetrate an remain in the surface of the wooden substrate. Accordingly, fractions of the concrete set solidly or the form board will frequently be flaked and remain adhered to the surface of the former or latter when they are removed after the complete curing of the placed concrete, rendering the board no more effective in repeated use or marring the appearance of the finished concrete.Some thermoplastic materials such as polyolefin including polyethylene and polypropylene have been found to exhibit satisfactory separation behavior when applied in the form of layer on the wooden substrate, that is, they are easy to be removed from a finished concrete without being flaked.

However, these thermoplastic materials are difficult to be adhered directly only by the application of heat and pressure on the surface of a substrate and even if.adhered in the form of layer which requires relatively long time for bonding by the application of heat and pressure, their bonding strength would be not enough for practical uses and be easily peeled off from the substrate on a construction site. While these easily accessible thermoplastic sheets can be coated on the substrate by a bonding agent, it remains a problem in manufacturing the form boards that any harmful solvent which may contain in the bonding agents will evaporate in the bonding process to jeopardise the working enviroment.

It has now been found, in accordance with this invention, that certain thermoplastic copolymer such as olefinic group copolymers, for example, acrylate denatured polyethylene copolymer, acrylate denatured polypropylene copolymer, ethylene vinylacetate copolymer, ethylene ethylacrylate copolymer, and the like, has higher bonding strength when directly adhered on the surface of a wooden substrate by the application of heat and pressure, as well as good separation performance when removed from the surface of a cured concrete.

These features are particularly useful in the forming of concrete structure where the concrete surface is exposed after the removal of concrete forms and the removed forms will be required to be used repeatedly. Such thermoplastic copolymer has also good water and chemical resisting properties which are desired for concrete forms to be used repeatedly.

Accordingly, it is a primary object of this invention to provide a coated board for concrete form with a covering of thermoplastic copolymer which is directly and firmly adhered on the surface of a wooden substrate but is easily removed from the surface of the set concrete, thus preventing the covering from being flaked or peeled off, when the board is removed from the set concrete, to give a designated finished surface of the concrete, and exerting durability for repeated use.

Another object of this invention is to provide a method of making the coated board wherein the layer or covering of the thermoplastic copolymer can be uniformly and fimly welded onto the surface of the wooden substrate without being warped in the solidification. Such warp of the thermoplastic layer would occur when thermoplastic materials once melted become solidified relatively rapidly on the substrate with the surface being exposed to the ambient air as is usual with the conventional process of manufacturing form boards having coverings of thermoplastic material bonded by the application of heat and pressure. That is, faster cooling of the.

melted thermoplastic material will cause the solidified material to shrink to a larger extent such that the layer or covering of the solidified material suffers a warp which may weaken the bonding strength between the layer of thermoplastic material and the substrate. In the method of present invention, the thermoplastic copolymer placed on the wooden substrate is covered with a release film or an outer layer of thermoplastic material having a higher melting point than that of the thermoplastic copolymer which is to be laminated directly on the substrate, and this placed layer of thermoplastic copolymer is protected with the release film or the outer layer from being exposed to the air throughout its welding process.Thus, the thermoplastic copolymer is subjected to slower cooling and has less shrinkage effect, which assures uniform and firm bonding of the layer of thermoplastic copolymer onto the surface of the wooden substrate.

Other objects and advantages of the present invention will be understood by reference to the following detailed description when considered in connection with the accompanying drawings in which: Figure 1 is a schematic sectional view of a coated board with a release film left according to a preferred embodiment of the present invention; Figure 2 is a schematic sectional view of a coated board with a release film left according to another preferred embodiment of the present invention; Figure 3 is a schematic perspective view of the part of the coated board shown in Fig. 2; Figure 4 is a schematic sectional view of a coated board without a release film according to a preferred embodiment of the present invention;; Figure 5 is a schematic view of a set-up useful in practicing the teachings of the present invention for feeding a composite material composed of thermoplastic copolymer sheet and thermoplastic polymer outer sheet on the substrate; Figure 6 is a schematic sectional view of a coated board in which the top veneer having a coating of thermoplastic copolymer is bonded together with a plurality of base veneers to form a plywood having the coated layer thereon; Figures 7 to 9 are schematic views showing respectively examples for coating the top veneer with a covering having a sheet of thermoplastic copolymer.

Referring to Fig. 1, the coated board according to one embodiment to the invention consists of a wooden substrate 1 and a layer or covering 2 adhered thereon. The wooden substrate 1 is a plywood of about 12 mm thick or may be other wooden material such particle board, fiberboard, and the like. The covering 2 is made of a high adhesive thermoplastic copolymer, i.e., an olefinic copolymer. Preferred olefinic copolymers are those which are produced by denaturing olefinic resins by acrylate, for example, acrylate denatured polyethylene copolymer, acrylate denatured polypropylene copolymer, ethylene vinylacetate copolymer (EVA), and ethylene ethylacrylate copolymer (EEA). The covering 2 is adhered onto the surface of the wooden substrate 1 by the application of heat and pressure.The covering 2 covers the entire upper surface of the wooden substrate 1, and the thickness of the covering 2 will depend on requirements on the construction site and is preferably about 0.1 to 0.2 mm. The covering material may contain antistatic and/or antidiscoloration agents. In the process of making the coated board, the high adhesive thermoplastic copolymer is placed onto the upper surface of the substrate 1 in the form of sheet or powder, thereafter, a release film 3 made of paper impregnated with silicone resin is applied on the sheet or layer of powder to sandwich the sheet or layer of the thermoplastic copolymer between the substrate 1 and the release film 3. Then this sandwich is heated to above the melting point of tile copolymer under the infuence of pressure to cause the copolymer to melt while leaving the release film 3 unmelted.After heating, this sandwich is left at room temperature with the film 3 being attached such that the melted copolymer will be cooled slowly to solidify or weld in the surface of the substrate 1. That is, the melted copolymer resolidifies with its top surface being protected by the film 3; thus, the melted copolymer is subjected to cooling without rapid heat release so as to undergo slower solidification, which will assure no substantial warp or the like or the covering 2 to be bonded on the substrate 1. Such warp would occurs when melted copolymer is cooled with its surface exposed to the air; in such condition, there would be developed much in the set copolymer internal stress due to the difference in the contraction rate between the copolymer and the wooden substrate, which will be the cause of the warp.Accordingly, the covering 2 is adhered uniformly and firmly to the substrate 1 and would not be peeled off or flaked when the board is removed from the surface engagement with cured concrete.

Once the covering 2 has been solidified, nor- maly it is completed within few seconds, the release film 3 may be peeled off anytime the covering adhered on the substrate 1. For example, it may be peeled off immeditly after the solidification of the covering 2, or may be peeled off on the construction site to protect the surface from being damaged before its end use. The release film may Qe a fabric impregnated with silicone and a silicone itself.

Figs 2 and 3 show another preferred em- bodiment of the present invention, in which outer layer 4 of a thercaoplastie n,aterial is laminated on the covering 2 of the thermoplastic copolymer. Said thermoplastic material forming the outer layer 4 must have a higher melting point than that of the copolymer forming the covering 2 and is an olefinic polymer produced from the corresponding monomer which is the base consitiuent of the above thermoplastic copolymer. That is, polyethylene is used as the material for the outer layer 4 when acrylate denatured polyethylene copolymer, ethylene vinylacetate copolymer, and ethylene ethylacrylate copolymer is used for covering 2, and polypropylene is used when acrylate denatured copolymer is used for the covering 2.Such olefinic polymers are preferably employed in the form of oriented film.

While the above thermoplastic copolymers retain excellent properties, such as in mechanical strength, chemical resistance, electrical insulation and the like, which are inherent to such olefinic polymers, and these copolymers melted will be incorporated in the corresponding olefinic polymers being softened, therefore, the melted copolymer is easy to be welded to the corresponding polymers when both are heated so as to melt the former and to soften the latter. The outer layer 4 and the covering 2 are applied on the substrate 1 in the form of sheet of about 0.1 mm thick with the latter being in contact with the upper surface of the substrate 1, and the abovementioned release film 3 is applied on the surface of the layer 4 to sandwich the outer layer 4 and the covering 2 between the release film 3 and the substrate 1.Subsequently, the sandwich thus formed is subjected to heat and pressure between the platens of a press to melt the covering copolymer and soften the outer layer polymer, and thereafter, it is cooled at room temperature to allow the melted copolymer to solidify and bond with the contacting surfaces of the substrate 1 and the outer layer 4. In this case, the outer layer 4 also acts together with the release film 3 to slow down the solidification rate to assure strong bonding of the covering 2 with the substrate 1 and the outer layer 4 for the same reason mentioned above. The release film 3, after the complete solidification of the covering copolymer, may be peeled off anytime when required.The covering material may be applied onto the substrate 1 in the form of sheet or powder, and in the former case, the covering sheet is preferably welded to the outer layer sheet 4 at appropriate spots in order to prevent possible slip between the sheets during the heat and pressure application.

Fig. 5 shows a preferred set-up for feeding and bonding the covering sheet 2 of the thermoplastic copolymer and outer layer sheet 4 of the inexpensive thermoplastic polymer onto the substrate 1. Each sheet 2, 4 is drawn from each roll 6, 7 of continuous length upon the surface of an upper roll 8 to become to be in contact with each other with the sheet 2 facing the substrate 1. The upper roll 8 is heated to have a surface temperature of above the melting point of the covering sheet 2.The above sheets 2, 4 being in contact with each other are then applied continuously onto the upper surface of the moving substrate 1 on a conveyor 9 and are pressed on the surface thereof between the upper roll 8 and a lower roll 10 having elastic outer surface, whereby the covering sheet 2 is subjected to heat and pressure from the upper roll 8 to become welded in the contacting surface of the outer sheet 4 and the substrate 1. The surface temperature and rotating speed of the upper roll 8 should be of course selected in accordance with the kind of sheet 2, 4 used and the surface condition of the substrate 1. The outer layer 4 acts also, as is previously stated, to slower the solidification of the covering material to provide strong bonding strength of the covering layer 2 to the substrate 1 and the outer layer 4.The sheets 2, 4 may be applied in the laminated form which is made by a suitable inflation process. In the above method, for preventing the adhesion of the outer layer 4 to the upper roll 8, the surface of the upper roll 8 may be treated with a fluorocarbon polymer or a suitable silicone release agent may be sprayed on the surface of the outer layer 4. The layers 2 and 4 thus continuously adhered on the substrate 1 will be cut finally to match with the contour of substrate 1 to provide the coated board as shown in Fig. 4, wherein the outer layer 4 is finished to have uniform thickness and the smooth surface.

Referring to Fig. 6, there is disclosed a coated board which is made of a top veneer 1 2 having a covering layer 2 of the high adhesive thermoplastic copolymer and a plurality of base veneer 1 3. Top and base veneers 12 and 13 are of 0.5 to 3 mm thick and bonded together by a suitable thermosetting plastic such as a meiamine resin and a diallyl phthalate resin in a common process employed for making plywoods. The thermoplastic copolymer may be applied in the form of powder or sheet of about 0.1 mm thick on the top veneer 12, and this covering material is bonded by the application of heat and pressure onto the top veneer 1 2. The covering layer 2 may be coated with the outer layer 4 of the thermoplastic polymer as mentioned previously.Fig. 7 indicates a structure of the coated top veneer 12, which is produced by the following steps of, placing a sheet 14 of the thermoplastic copolymer on the top veneer 12, scattering a release agent such as silicone in the form of powder or emulsion thereof uniformly on the entire upper surface of the veneer 1 2 to cover the sheet 1 4 with the layer 16 of the release agent, and applying pressure and heat to this layered product between the upper and lower platens 1 6 and 17 of a press to melt the thermoplastic copolymer whereby the thermoplastic copolymer bonds to the top veneer 12 as being resolidified to form a covering layer 2. The upper platens 16 can be easily removed from the surface of the covering layer thus formed with the help of the above release agent.Figs. 8 and 9 show other structures of the coated top veneer 12 having the composite covering composed of the thermoplastic copolymer layer 2 and the corresponding thermoplastic polymer layer 4 of the kind described hereinbefore. Each layer is applied in the form of sheet 18, 19 onto the top veneer 12; the layered product is then subjected to heat and pressure between the platens 16 and 17 in order to bond the outer layer sheet 19 on the top veneer 1 2 via the covering layer 18 of the thermoplastic copolymer which is welded in both the top veneer 1 2 and the sheet 1 9. For easy removing the upper platen 16 from the finished surface of the coated top veneer 12, the release film 3 of silcone may be superimposed on the entire surface of the sheet 16 as indicated in Fig. 8, or the emulsion 20 of the release agent is coated on the entire surface of the sheet 19 as indicated in Fig. 9.The coated top board thus prepared is thereafter laminated together with a plurality of base veneers 13 by using the above mentioned thermosetting materials indicated by the numeral 22 in Fig. 6 as an adhesive to form a coated plywood having a covering layer 2 of the thermoplastic copolymer. In this processs of laminating by applying heat and pressure, the covering 2 which has already set on the top veneer 12 will again receive heat and pressure, which serves to enhance surface eveness and close adhesion of the covering 2 to the substrate or the top veneer 12.Therefore, even if the covering 2 is not bonded strongly enough in the process of laminating the covering layer 2 to the top veneer 12, that is, if there may be some spots in the covering layer 2 failing to weld in the surface of the top veneer 12, this process of making the plywood provides additional heat and pressure to the possibly defective covering layer 2 so as to be completely adhered to the top veneer 12.

To further illustrate the present invention, and not by way of limitation, the following examples are given.

Example 1 A sheet of 0.1 mm thick high adhesive thermoplastic copolymer, which is the acrylate denatured polyethylene having a melting point of about 125 C and being sold under the trade name of CMP-HASO by Tonen Petroche mical Industries Ltd. Japan, was placed on 12 mm thick plywood measuring 900 mm by 1800 mm, and a release film made of paper impegnated with silicone, which is sold under the trade name of DN-TP-APZ-S(DE-3) and has a weight of 1 30 g/cm3, was superimposed evenly on the entire suface st' the sheet. Then the layered product was heated to a temperature of 1 70 C under a pressure of 8kg/cm2 between the platens of a press for 2 minutes.

In this process deaeration may be made when required. After cooling of few seconds at room temperature, the release film was removed from the surface of the copolymer adhered on the plywood.

Example 2 A sheet of Q.1 mm thich low pressure polyethylene sheet having a melting point of 1 90 C and the same sheet of high adhesive thermoplastic copolymer (C:MP-HA50) employed in example 1 were superimposed upon a plywood of the same dimensions in example 1 such that the sheet of the above copolymer was sandwiched between the polyethylene sheet and the plywood, and a release paper as above was applied on the polyethylene sheet.

Then, the layered product was heated to a temperature of 1 70 C under a pressure of 12 kg/cm2 for 3 minutes between the same platens as in example 1. Few seconds after cooling at room temperature, the release film was removed from the surface of the polyethylene sheet adhered via the sheet of copolymer to the plywood.

Example 3 The same procedure described in example 2 was repeated except that polyethylene sheet having a melting point of 1 50 C was used and that a layered product was heated to a temperature of 1 60 C.

Example 4 A sheet of 0.1 mm thick high adhesive thermoplastic copolymer, which is the acrylate denatured polypropylene having a melting point of about a27"C and being sold under the trade means of CMP-HA20 by the above company, was placed on a plywood of the same dimensions as in example 1. The same release film as in example 1 was thereafter applied throughout the surface of the sheet.

Then, the layered product was heated to a temperature of 1 90 C under a pressure of 1 5 kg/cm2 for 3 minutes using the same press as in example 1. After cooling a few seconds, the release film was removed frcm the surface of the sheet adhered on the plywood.

Example 5 A sheet of 0.1 mm thick thi@k high adhesive thermoplastic copolymer, which is ethlene vinylacetate (EVA) having a melting joint of 95 C, was placed on a plywood of the same dimensions as above, the same release ,íim was applied on the entire surface of the she9^.

Then, the layered product was heated to S temperature of 130 C under a pressure of 10 kg/cm for 2 minutes in the same @@@@@ as in example 4. Few seconds after cooling at room temperature, the release film was removed from the surface of the sheet adhered on the plywood.

Example 6 The same procedures described in example 5 were repeated except that the high adhesive thermoplastic is ethylene ethylacrylate (EEA) having a melting point of 90"C to produce a plywood with the covering of EEA thereon.

Example 7 A sheet of 0.1 mm thick high adhesive copolymer, which is acrylate denatured polyethylene having a melting point of 90"C and being sold under the trade name of ADMER VE300 by Mitsui Petrochemical Industries Ltd. Japan, and a sheet of 0.1 mm thick medium pressure polyethylene having a melting point of 1 80 C were superposed upon each other, and this composite of two different sheets was introduced onto the upper surface of a plywood of 1 2 mm thick by means of a rotating and heating roll, the surface of which was finished with a fluorocarbon polymer and the temperature of which was maintained at 230"C. Subsequently, the above composite was compressed onto the upper surface of the plywood between the rotating and heating roll and a roll being in rolling contact with the lower surface of the plywood while the plywood was leaving the roll at a speed of 20 m/min.

Example 8 The same procedure was repeated described in example 7 except that the high adhesive thermoplastic copolymer is acrylate denatured polypropylene having a melting point of 1 20 C and being sold under the trade name of ADMER NE050 by the above company in place of the sheet of ADMER VE300, and a polypropylene sheet having a melting point of 200"C is employed in place of the polyethylene sheet. The heating roll was heated to have a surface temperature of 250"C and the plywood was leaving the roll at a speed of 30 m/min.

Example 9 The same procedure was repeated described in example 7 except that the high having a melting point of 1 50 C was employed and that the surface temperature of the heating roll was mainitained at 1 90 C.

Example 10 A composite sheet produced by an inflation process composed of a sheet of 0.1 mm thick adhesive thermoplastic copolymer, which is acrylate denatured polyethylene having a melting point of 123"C and being sold under the trade name of CMP-HA4O by Tonen Petrochemical Industries Ltd. Japan, and a sheet of 0.1 mm thich polyethylene having a melting point of 175"C was introduced and thereafter compressed onto a plywood of 1 2 mm thick in the same manner as described in example 7. The heating roll was heated to have surface temperature of 230 C and the plywood coated with the composite was leaving the mi at a speed of 30 m/min.

Example 11 The same procedures described in example 7, 8, 9 and 10 were repeated respectively on particle boards of 10 mm thick Example 1 2 The same procedures described in example 7, 8, 9 and 10 were repeated respectively on fiberboards of 10 mm thick.

Example 13 The same procedures described in example 10 were repeated on a plywood of 1 2 mm by using a iron-made heating roll without being finished with a fluorocarbon polymer exept that a silicone-impregnated release paper of 1 30 g/cm3, which is sold under the trade name of DN-TP-APZ-S(DE-3), was applied upon the above composite. The release paper was removed from the composite adhered on the plywood few minutes after the plywood had left the roll.

Example 14 The same sheet of high adesive thermoplastic copolymer as employed in example 1 was placed onto the entire upper surface of 1.6 mm thick veneer measuring 900 mm by 1 800 mm, and a release agent powder, which is sold under the trade name of Lubron L-5 by Daikin Kogyo Co., Ltd. Japan was scattered evenly on the entire surface of the sheet. Subsequently, the veneer with the sheet and release agent powder thereon was heated with the sheet and release agent powder thereon was heated to a temperature of 1 60 C under a pressure of 5 kg/cm between the platens of a press for 30 seconds.Few seconds after cooling at room temperature, the veneer with the sheet welded thereon and a plurality of veneers of the same dimensions were bonded by melamine resin as an adhesive at temperature of 1 20 C for 50 minutes under a pressure of 10 kg/cm2 to form a plywood having a coated layer of the above copolymer thereupon.

Example 15 The same high adhesive thermoplastic sheet as employed in example 1 and a sheet of 0.1 mm thick low pressure polyethylene polymer having a melting point of 1 90 C were superimposed on a 1.6 mm thick veneer measuring 900 mm by 1800 mm such that a copolymer sheet was sandwiched between the ethylene polymer sheet and the veneer, and then the same release paper as in example 1 3 was placed on the entire surface of the ethylene sheet. Thereafter, the layered product thus formed was heated to a temperature of 1 70 C under a pressure of 10 kg/cm2 for 40 seconds between the plates of a press. The same procedure described in example 14 was repeated with thus coated veneer to form a plywood with the corresponding coated layer thereon.

Example 16 The same layered product as described in example 1 5 was prepared except that an emulsion of silicone being sold under the trade name of KM 742 by Shin-etsu Chemical Industry Co., Ltd. Japan was scattered evenly on the entire surface of the polyethylene sheet in place of release agent powder. Then this layered product was treated with the same procedure as described in example 11 to form a plywood having the coated layer thereon.

All the coated layers thus formed on the substates according to the above examples could not be peeled off the substrates manually and are found to have superior properties in bonding strength and surface evenness to those of the conventional concrete form boards in which thermoplastic polymer covering is directly adhered on the same substrate by the application of heat and pressure, and still to retain the same properties in waterresisting, surface hardness etc. as those of the conventional boards with the thermoplastic polymer covering. Therefore, the coated board of the present invention is to be noted to have durability for repeated use many times that of the conventional concrete form boards.

The high adhesive thermoplastic copolymer employed may contain acid anhydride such as maleic acid anhydride and pthalic acid anhydride. The thickness of covering layer and other dimensions will vary within the usual sense of the art in accordance with a designated use and should not be understood to be limited to the above description.

Claims (12)

1. A coated board for concrete forms which comprises, a wooden substrate including plywood, particle board, fiberboard, and the like; and a layer of high adhesive thermoplastic copolymer welded on the upper surface of the wooden substrate; said high adhesive thermoplastic copolymer is an olefinic copolymer and is selected from the group consisting of acrylate denatured polyethylene copolymer, acrylate denatured polypropylene copolymer, ethylene vinylacetate copolymer, and ethylene ethylacrylate copolymer.

2. The coated board for concrete forms as set forth in claim 1, further comprising outer layer of thermoplastic material which has a higher melting point than that of said high adhesive thermoplastic copolymer, the outer layer consisting the entire surface of the layer of thermoplastic copolymer.

3. The coated board for concrete forms set forth in claim 2, wherein said thermoplastic material is an olefinic polymer produced from the corresponding monomer which is the base constituent of said thermoplastic copolymer.

4. A method of making a coated board which comprises, applying a high adhesive thermoplastic copolymer onto the surface of a wooden substrate including plywood, particle board, fiberboard, and the like; covering a layer of the thermoplastic copolymer with a release film to sandwich the layer of the thermplastic copolymer between the wooden substrate and the release film; applying heat and pressure to this sandwich so as to melt the thermoplastic copolymer while leaving the release film unmelted; cooling at room temperatures the sandwich with the release film being attached so as to allow the melted copolymer to solidify and weld in the surface of the wooden substrate; and stripping the release film off a thermoplastic copolymer layer formed on the wooden substrate.

5. The substrate as set forth in claim 4, wherein said thermoplastic copolymer is applied in the form of sheet onto the surface of the wooden substrate.

6. The method as set forth ill claim 4, wherein said thermoplastic copolymer is applied in the form of powder onto the surface of the wooden substrate.

7. The method as set forth in any one of claims 4-6, wherein said thermoplastic copolymer is selected from the group consisting of acrylate denatured polyethylene copolymer, acrylate denatured polyproplene copolymer, ethylene vinylacetate copolymer, and ethylene ethylacrylate copolymer.

8. The method of making a coated board which comprises, applying a sheet of high adhesive thermoplastic copolymer onto the surface of a wooden substrate including plywood, particle board, fiberboard, and the like; covering the sheet of said thermoplastic copolymer with an outer sheet of a thermoplastic material having a higher melting point than that of said high adhesive thermoplastic copolymer so as to sandwich the sheet of the copolymer between the outer sheet and the wooden substrate; applying heat and pressure to this sandwich so as to melt the sheet of the thermoplastic copolymer while softening the outer sheet; cooling this sandwich at room temperature to allow the once melted thermoplastic copolymer to solidify and weld both in the contacting surfaces of the substrate and the outer sheet.

9. The method as set forth in claim 8, wherein the sheet of said thermoplastic copolymer and the outer sheet of said thermoplastic material is welded together at appropriate spots so as to be placed on the the substrate in the combined form.

10. The method as set forth in any one of claims 8 or 9, wherein said thermoplastic copolymer is selected from the group consisting of acrylate denatured polyethylene copolymer, acrylate denatured polypropylene copolymer, ethylene vinylacetate copolymer, and the ethylene ethylacrylate copolymer; and said thermoplastic material forming the outer sheet is an olefinic polymer produced from the corresponding monomer which is the base constituent of said thermoplastic copolymer.

11. The coated board for concrete forms substantially as described with reference to the accompanying drawings.

1 2. The method substantially as hereinbefore described with reference to the Examples.

1 3. A coated board made by a method as claimed in any of claims 4 to 10, or claim

1 2.