EP0309606A1

EP0309606A1 - Improved concrete form panel product

Info

Publication number: EP0309606A1
Application number: EP87114346A
Authority: EP
Inventors: Leonard J. Annaloro
Original assignee: Weyerhaeuser Co
Current assignee: Weyerhaeuser Co
Priority date: 1987-10-01
Filing date: 1987-10-01
Publication date: 1989-04-05

Abstract

A composite wood based concrete form panel product (10) is made using an oriented strand type wood based panel product (12,14,16) which is then overlaid with a suitably selected polymeric material (18,20) to completely encapsulate the wood based substrate. The oriented strand type substrate gives excellent stiffness characteristics while the polymeric material which is adhered to the wood surfaces by a suitable adhesive such as a hot melt type epoxy will give long life and good durability to the concrete form panel product. Suitable release agents and antiskid materials can be incorporated into the polymeric material and in addition, the polymeric material can be stabilized to ultraviolet radiation to also increase its life. In those cases where the encapsulated concrete form panel product will be cut in the field a liquid polyurethane based material should be used to reseal the cut edge and again encapsulate the entire wood based substrate material.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to relatively large flat panel products that are used to create the form structure or mold for supporting a concrete pour during the pouring and curing stage. More particularly, it relates to a composite wood based panel product with improved stiffness and durability properties for use as a concrete form or mold member.
In the past one basic element used in making concrete forms or molds has been the relatively flat panel. One of the early panel products used for concrete forms was ordinary plywood, layers of wood veneer laid up to form relatively stiff panels. Early it was recognized that when untreated wood was used the grain pattern would be left on the concrete face and further that whatever defects were on the face of the plywood panel they too would appear on the face of the concrete. In addition, the basic plywood panels were not able to be reused more than three or four times before they lost their properties and usefulness as concrete form members.
Consequently, it became necessary to begin treating the standard panel products used as concrete forms with various coatings to improve surface quality, releasability, durability, and other suitable properties. Now it is the basic standard plywood panel but one which is treated that is being used as the basic wood based panel for making concrete forms.
One commercially available plywood based composite concrete form panel is the overlaid product where resin impregnated heavy paper is overlaid against the surfaces of the plywood substrate and then cured to form the so-called medium and high density overlaid concrete form panel products. In recent years another new product has been introduced with greater strength properties than typical treated plywood simply by adding additional layers of veneer so that the multilayered product has from 10 to 15 layers of veneer. This plywood panel product then is sealed on both faces by the impregnation of phenolic resins prior to the application of phenolic plastic faces applied in a hot press. The edges in this concrete form panel product are sealed to inhibit moisture penetration.
A new composite wood based panel product has been introduced recently that has now been found to make an excellent substrate for the manufacture of composite concrete form panel products. Problems with existing concrete form panel products, as previously noted, also include the lack of complete moisture resistance, the lack of structural stiffness, and cost. It has been found with the product of the present invention that enhanced properties are generated as are lower manufacturing costs to produce a very stiff, moisture resistant, highly reusable, durable concrete form panel product.
Thus, from the foregoing, one object of the present invention is to provide a stiffer concrete form panel product and one that is capable of being reused time and time again.
A further object of the present invention is to provide a completely sealed wood based substrate that utilizes components specifically selected for contact with concrete.
These and many other objects of the present invention will become more apparent upon reading the specification to follow in conjunction with the attached drawing.

BRIEF SUMMARY OF THE INVENTION

Briefly stated, this invention is practiced in one form by encapsulating or completely covering the surfaces of a wood based panel product that has predetermined stiffness properties greater than those of state-of-the-art wood based substrates. The encapsulation includes at least a polymer overlay with the polymer of choice being a vinyl material covering both large surfaces and affixed to the underlying wood faces with en epoxy based adhesive. Preferably the polymeric material has incorporated therein a concrete release agent. In addition, the polymeric material is stabilized to the exposure of ultraviolet radiation. In one embodiment of the improved product, the four edges are also covered with a polymeric material, preferably vinyl, and adhered thereto with a hot melt type of adhesive. The resulting product is the completely encapsulated wood based concrete form panel product.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a partially cut away isomeric view of the improved panel product.
Figure 2 is a cross-sectional view taken along line 2-2 of Figure 1 and shows the wood based substrate material with the polymeric material completely encapsulating the substrate.
Figure 3 is also a cross-sectional view taken along line 3-3 of Figure 1 similarly depicting that the end edges of the composite product have the polymeric material covering them to completely encapsulate the wood based substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning first to the figures, the basic structure of the present product will be described. In Figure 1 the planar form of the composite wood based concrete form panel product is generally indicated at 10. The most typical size for these concrete form panel products is 4′ x 8′. As will become apparent, the present product can be manufactured in different sizes, particularly in view of the type of wood based substrate that is used in its manufacturing process. The wood based substrate material is a commercially available product manufactured and sold by the assignee of the present invention under the trademark "STRUCTURWOOD" and includes at least three distinct layers with each layer comprised of oriented strands of wood particles bonded together with a phenolic based adhesive system. These wood based panel products are generally referred to in the industry as oriented strandboards or oriented flakeboards. Briefly they are manufactured by generating the elongated wood particles or strands and then usually in a continuous manufacturing process sequentially creating the layer on a traveling screen at orienting stations where the face layers will have the strands generally oriented in the longer dimension while the inner ply will have its strands oriented in a crosswise direction, substantially perpendicular, to the direction of the strands in the face layers. The analogy is to a three-ply sheet of typical plywood. Prior to orienting the strands in the respective layers, the suitable adhesive is incorporated either as a spray or in other suitable form so that once the loosely compacted mat is formed it may then be directed to the pressing apparatus for consolidation and curing of the adhesive. Upon the application of heat and pressure in the press for a sufficient time, the resin cures and the panel is pressed to its final predetermined thickness at the preselected density.
As will be appreciated by those skilled in the wood based composite panel manufacturing art, these types of panel products can be manufactured in varying thicknesses depending upon the ultimate end use and additionally, they can be pressed into various widths and lengths depending upon the dimensions of the press being utilized. Plywood panels, on the other hand, are generally pressed to the typical 4′ x 8′ size in a multi-opening vertically stacked press.

Representative values for the Weyerhaeuser Company STRUCTURWOOD product are contained in the following tables.

TABLE I

Stress Applied Parallel To Face Flake Orientation

Stress Applied Perpendicular To Face Flake Orientation

Flatwise Bending
f_b	1,800 psi	950 psi
E	1,350,000 psi	500,000 psi

Edgewise Bending
f_b	1,350 psi	1,050 psi
E	850,000 psi	500,000 psi

Tension
f_t	900 psi	550 psi
Values Shown: Normal 10-year Load Duration
Dry End Use Conditions

TABLE II

Properties to Be Used with Structurwood Design Values
Normal Thickness	Moment of Inertia (in. 4/ft.)	Section Modulus (in. 3/ft.)	Thickness For Tension and Edge Binding (in.)
7/16"	0.084	0.383	0.438
1/2"	0.125	0.500	0.500
9/16"	0.178	0.633	0.563
19/32"	0.209	0.705	0.594
5/8"	0.244	0.781	0.625
23/32"	0.371	1.033	0.719
3/4"	0.422	1.125	0.750

TABLE III

PERFORMANCE
Relative to Commonly Accepted Standards of Industrial Market Segment
Properties	ANSI A 208.1	Structurwood*
MOR psi	2,500	5,500
MOE psi	450,000	1,000,000
Internal Bond psi	50	60

Screw Holding lbs.
-Face	250	325
-Edge	200	240
Density lbs/cf	36+	36-40
Thickness tolerance, in.	± 0.030	± 0.032
Linear Expansion %	0.20	0.1

It can be noted from these tables that the oriented strand panel product has very good properties. Thus, the wood based substrate used in the manufacture of the present improved product directly yields the increased stiffness values for the completed composite concrete from panel product. Another advantage in utilizing an oriented strand type product for the substrate is the uniformity in the surface, flatness and appearance owing to the use of the strands and pressing process. When using plywood type substrates, oftentimes there are knot holes and other defects present in the surface layers which can carry visual defects into the surface of the finished concrete.
As seen in Figure 1, the definitive layers of oriented strand material are designated by reference numerals 12, 14 and 16. The individual strands in core layer 14 run substantially perpendicular to those in outer layers 12 and 16. In the final concrete form panel product as depicted in Figures 2 and 3, both upper and lower flat surfaces will have securely attached thereto a polymeric material covering the entire surface and depicted as polymeric layers 18 and 20. Additionally, the long side edges are also covered with a layer of the same polymeric material with the long strips being indicated at 22 and 24. These layers of polymeric material are bonded to the respective surfaces of the oriented strand wood based substrate by the use of suitable adhesive which in the preferred embodiment is a hot melt epoxy type adhesive that is highly moisture resistant and provides a complete bond between the polymeric material and the surface of the wood based substrate. Any suitable method for attaching the polymeric surface layers to the wood based substrate may be utilized, such as by spraying or rolling the epoxy adhesive on the wood surfaces and then laminating the polymeric material thereto. In the preferred alternative the adhesive is coated onto the polymeric material and then laminated to the substrate.
In the preferred embodiment, the polymeric material is selected from commercially available vinyl and is selected, in part, based on its thicknesses. In one embodiment, the thickness of the vinyl material is .020 inches while in another embodiment the polymeric material is a thickness of .030 inches. Incorporated into the polymeric material should be a suitable release agent for allowing the concrete form panel product to easily separate from the concrete. In addition, the polymeric material should be suitably stabilized by an ultraviolet treatment to reduce degradation from sunlight since in the past radiation from the sun tends to cause blistering and delamination in composite state-of-the-art concrete form panel products. For the normal application, the polymeric surface layers will be smooth providing a smooth surface against the concrete being cured. In another embodiment, however, additional texturing material can be added to the polymeric material to provide an antiskid surface to the surface layers of the concrete form panel product. These will normally be added to the polymeric material that is thicker and, of course, when incorporated and used at a construction site will result in improved antiskid properties.
As may be seen in Figure 2, the polymeric material is shown being applied to one large surface and having edges extending outwardly which are then wrapped upwardly to encapsulate the longer side edges of the wood based substrate material. In this embodiment, then, the upper surface 18 has affixed thereto a single sheet of polymeric material that dimensionally will coincide with the dimensions of the wood based substrate material but with some added to overlap the narrow edges of the polymeric material that extends along the long edges of the wood based substrate. With such a product, there are no joints in the polymeric material along the edges on one surface of the wood based substrate.
In the embodiment depicted in Figure 3 the upper and lower larger surfaces and the long side edges of the wood based substrate are covered with the polymeric material that covers the respective surfaces. In covering the shorter end edges of the wood based substrate material, individual strips 26 and 28 of polymeric material will be used but all individual pieces of polymeric material will be sized so that when the composite product is complete, while there will be joints, the wood based substrate material will be completely encapsulated by polymeric material. This encapsulation process results in the completely covered wood based substrate that is highly resistant to moisture penetration and adds significantly to the useful life of the wood based concrete form panel product.
It will be appreciated by those skilled in the art that suitable polymeric materials, in particular, special sheet vinyl products are commercially available from suppliers such as B. F. Goodrich, as are the suitable adhesive products and, in particular, epoxy type products which are available from manufacturers such as Daubert Chemical Co.

When the improved concrete form panel products of the present invention are required to be cut in the field, therefore exposing a wood based edge, a liquid polyurethane based sealer should be applied to the exposed edge to re-encapsulate the entire wood based substrate. Again, suitable liquid polyurethane sealers are commercially available and may be obtained from a manufacturer such as Daubert Chemical Co. In the following table, stiffness comparisons are presented for several different product thicknesses with the product constructed according to the present invention having the values in the column identified as STRUCTURWOOD. The column identified as Reg HDO represents values for a high density overlaid type concrete panel product while the column identified as MDO B-Matte is a medium density overlaid product. The three columns, Class 1, Class 2, and Struc-I under the column identified as BB Plyform Grades represent the more typical plywood type concrete form panel products that have the wood surfaces treated but not overlaid with any additional material. The column identified as Finn Form shows the values for a plywood type substrate having 10-15 veneer layers and then having additional plastic faces applied thereto.

TABLE IV

STIFFNESS COMPARISONS
EI in sq. in-lbs
Thickness Inch	STRUCTURWOOD	Reg HDO	MDO B-Matte	BB Plyform Grades		Struc-1	Finn Form
				Class 1	Class 2
1/2	168,750	132,000	132,000	127,000	107,000	129,000	142,000
5/8	329,400	238,500	238,500	195,000	185,900	216,100	304,000
3/4	569,700	394,500	360,000	328,300	283,140	333,300	489,000

In terms of stiffness values, it will be seen the values for the STRUCTURWOOD product and those for the Finn form product are comparable, but the Finn Form product is much costlier to manufacture and may not provide the same reusability and useful life that the STRUCTURWOOD product provides. It is expected that the product of the present invention with the relatively thinner vinyl covering when proper care is taken will be able to be reused many times while the product having the thicker vinly covering is expected to have a reuse factor of perhaps up to 200 times. This is primarily because of the toughness and durability of the selected polymeric material and the adhesives used to bond the polymeric material to the surfaces of the wood based oriented strand type substrate. Due to the overall lower cost of the oriented strand type substrate material, tougher more durable polymeric sheet material can be used, together with the epoxy type adhesives, resulting in an overall stiffer and more durable concrete form panel product capable of significantly greater reusability at reasonable prices. Given the type of composite structure of the wood based substrate, no gaps or wood grain will appear on the surface of the concrete. Since the oriented strand type of wood based panel can be manufactured in longer lengths (longer than the typical 8-foot length for plywood panels), longer composite products made according to the present invention can be fabricated which can then result in fewer joints appearing along the surface of the concrete being formed. In addition, since the wood based substrate material is completely encapsulated by the polymeric material, moisture buildup is substantially eliminated, thereby adding to the life of the product and increasing the reusability.
Having described in detail the present invention and several embodiments, it may occur to others having ordinary skill in the art to make modifications not disclosed herein. All embodiments described herein and those obvious from the description are intended to be included within the scope of the appended claims.

Claims

1. A wood based panel useful as a concrete form panel, comprising:
a plurality of elongated oriented strands of wood particles bonded together with a water resistant adhesive system forming at least one discrete layer in the panel with the resulting panel having two large substantially flat surfaces and substantially flat side edges,
layers of a polymeric overlay material bonded to each large surface and at least some of the side edges with a hot melt type epoxy adhesive whereby substantially all surfaces of the panel are encapsulated within the layers of polymeric overlay material.

2. The panel of claim 1 in which the polymeric material is a vinyl.

3. The panel of claim 1 in which a concrete release agent is incorporated into the polymeric material.

4. The panel of claim 1 in which the polymeric material is stabilized to the exposure of ultraviolet radiation.

5. The panel of claim 1 in which the polymeric material has an antiskid material incorporated therein.

6. The panel of claim 1 in which the stiffness properties of the underlying wood based panel are predetermined.