AU594246B2 - Reinforced plastic composite/wood product laminate structures - Google Patents

Description

r 5942& FRef:4885 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SIPECIFICATION ThY3 documeat wntaina the Im ondmests mnds ane S3cWoa 49.

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FOR OFFICE USE: Class Int Class Complete Specification Lodged: Accepted: Published: Priority: 9990 *r 9, 99 9 9 9 9 99 99 9 99 9 99C .9 9.

*r 9i Related Art: Name and Address of Applicant: Address for Service: The Dow Chemical Company 2030 Dow Center, Abbott Road Midland Michigan 48640 UNITED STATES OF AMERICA Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: Reinforced Plastic Composite/Wood Product Laminate Structures The following statement is a full description best method of performing it known to me/us of this invention, including the

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ABSTRACT

A laminate comprising a base layer of a wood product and at least one dry mat composite layer bonded thereto by heat and pressure, the composite layer comprising, based on layer weight, from 10 to 50 percent by weight of cellulose fibers, from 10 to 89 percent by weight of a solid heat-fusible polymer in particulate form, and from 1 to 80 percent by weight of a binder, the bonding between the composite layer being sufficiently strong to preclude removal of the composite layer as a single, contiguous sheet.

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PLASTIC COMPOSITE/WOOD LAMINATE STRUCTURES *s S 9 a* 5 I it 1 I i i a I(i Ea i (P it D i Ct The present invention generally concerns laminate structures having a wood product core having at least one thermoplastic polymer composite layer bonded to at least one of its major planar surfaces without the use of an intermediate adhesive layer. The present invention more particularly concerns such structures wherein the thermoplastic composite layer contains randomly distributed and oriented cellulose fibers and an amount of a binder.

Plastic overlays for wood products, such as high-pressure laminated sheets of melamine and phenolic plastics, sold under the trade name Formica'M, are used in a variety of decorative applications. In these applications, one must use an adhesive which bonds to both the wood or wood product and the overlay. These adhesives, while expensive, do not have an indefinite 20 life. When they fail, the overlay readily delaminates from its substrate, as a single contiguous sheet, with the application of a separating force.

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"Al -2- 0000 0 0 0 04 4 *0 0 00 00 0 *0~.09 0 0 4*00 0 0 0090 09 0 0 44 0 00 04 04 0 4t 44 4* 4, 04 4 t~ 0 4~ 04 .4 0 4~ Polymer film layers, such as those formed from polyethylene or polypropylene, do not bond well to a wooden substrate even with an adhesive. In addition, such films are relatively soft and waxy thereby rendering them susceptible to abrasion and scoring.

Furthermore, if these films have sufficient strength or integrity, they can generally be pulled away from their wood product substrate without tearing by a 1800 peel.

Phenolic paper overlays for wood are not water resistant arid have limited abrasion resistance.

Because of their poor water resistance, they must be oiled before being used as a concrete pouring form.

Before being reused, they must be checked for tearing, cleaned and oiled again. Even then, some concrete surfaces are not as smooth as desired for certain applicat ions.

Daily et al Patent No. 4,481,075) teach 20 preparation of a sheet by paper-making techniques from an aqueous suspension of cellulosic fibers, a powdered, thermoplastic polymer, a binding agent and a flocculant. Such a sheet is said to be useful as a 25 support for coating of plasticized PVC for ground covering when the thermoplastic substance introduced into the sheet is PVC and the sheet is filled an~d plasticized. In other words, these sheets bond to~ like materials.

Wessling et al Patent No. 4 42 6, 47 0) teach that reinforced polymer composites having a uniform mix of fiber, polymer and binder and having good physical properties are prepared by forming dilute aqueous slurries of a solid heat-fusible organic polymer, a reinforcing material and a bound-charge 4 35,755-F -2-

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7 -16- -3latex binder. These composites can be fabricated by conventional methods such as, for example, compression molding, continuous double belt thermal press, stamping and scrapless forming processes. Several layers of the composite can be pressed together in a steam heated press to form a hard flat plate.

Eichhorn et al Patent No. 4,596,736) teach laminated structures prepared from a substantially nonreinforced polymer core and outer layers comprising a resin containing randomly oriented reinforcing fibers.

Yats Patept No. 4,550,131) discloses preparation of- a polymeric composite in the absence of a flocculant comprising the steps of forming an 94 0 alkaline aqueous slurry comprising a reinforcing material, a heat-fusible organic polymer and a binder Sto *9* 9 9 "comprising a salt of an ethylene acrylic acid copolymer 20 and thereafter adjusting the pH of the slurry such that *the binder is destabilized to coagulate the slurry.

SThe destabilized slurry is then collected in the form of a mat, dewatered and dried. The dried mat can be St 25 used in the same manner as the mat disclosed by Wessling et al.

It would be desirable to have a polymeric sheet material which would bond strongly to a wood product substrate without requiring an intermediate adhesive t layer.

It would also be desiraole to have such a polymeric sheet material which had sufficient abrasion °a and water resistance to be useful in applications such as concrete forms.

S35,755F -3- I L -4- One aspect of the present invention is a wood product laminate comprising a base layer of a wood product and at least one composite layer bonded thereto by heat and pressure, the composite layer comprises a dried mat which comprises, based upon layer weight, from 10 to 50 percent by weight of cellulose fibers, from 10 to 89 percent by weight of a solid heat-fusible polymer in particulate form, and from 1 to 80 percent by weight of a binder, the bonding between the composite layer being sufficiently strong to preclude removal of the composite layer as a single, contiguous sheet.

The bonding between the composite layer and the wood product layer is sufficiently strong to preclude removal of the composite layer as a single, contiguous sheet.

A related aspect of the present invention is such a laminate wherein a thermoplastic polymer film layer is interposed between the base layer and the composite layer.

A second related aspect of the present invention is such a laminate wherein a thermoplastic polymer film layer is interposed between the base layer and the composite layer, the latter being filled with a particulate filler material in an amount of from about five to about eighty percent by weight, based upon combined weight of filler material, cellulose fibers and heat-fusible polymer.

A third related aspect of the present invention is such a laminate wherein a filled composite layer is superimposed on, and bonded to by application of heat and pressure, the composite layer, said filled composite layer being filled with a particulate filler material in an amount of from about five to about et M 1C

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8 8984 88 8 8* 8 8 84; 'Cr I tt $8r 8 i eighty percent by weight, based upon combined weight of filler material, cellulose fibers and heat-fusible polymer.

The composite layer is suitably prepared by a process similar to those disclosed in U.S. Patent Numbers 4f426,470 and 4,481,075. In particular, the cellulose fibers are intensely mixed with water in a refining apparatus until a generally uniform dispersion is obtained. While continuing the intense mixing action of the refiner, the binder and then the heatfusible polymer are added to, and distributed throughout, the uniform dispersion. The dispersion is then destabilized, either by adding a flocculant where required or by adjusting the pH of the dispersion, thereby causing solid components of the dispersion to agglomerate so they can be collected, dewatered, formed into a sheet, if desired, and dried.

With less than about 10 percent by weight of cellulose fiber, and in the absence of fibrous material such as a polyolefin pulp, formation of a mat is quite difficult, if not impossible. Although mats can be 25 formed with greater than about 50 percent by weight of cellulose fiber, such mats are not suitable for purposes of the present in;ention for two reasons.

First, they do not adhere well to the wood product base layer. Second, they delaminate from the base layer as a generally contiguous layer when a sharp instrument, such as a screwdriver, is inserted between the composite layer and the base layer and used to pry the layers apart. By way of contrast, composite layers having a cellulose fiber content of from 10 and percent by weight, particularly where the fibers are softwood fibers, generally cannot be separated from the

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ft 1 ft 41 ~4 Oft I *4 0* 4 4 Itt If the amount of binder is less than 1 percent by weight, there is insufficient material to bind the solid, heat-fusible particles and the cellulose fibers.

Although the binder may be present in amounts of up to percent by weight, such high quantities are oot necessary. As the binder content of the composite layer increases above 10 weight percent, the binder begins to function like the heat-fusible particles in that it forms part of the matrix which holds the cellulose fibers in place. While this is not undesirable, the heat-fusible particles are more efficient kn terms of matrix formation. The amount of 20 binder is desirably from 1 to 10, preferably from 2 to 7, percent by weight of the composite layer.

If the binder is a salt of an ethylene/acrylic acid copolymer having an acryrlic acid content of from 25 12 to 30 percent by weight of' copolymer solids, the amount of binder is beneficially from 1 to 6, and desirably from 1 to 4, percent by weight of the composite layer. It has been observed that amounts in excess of 6 percent by weight lead to undesirably high levels of foanaing in the refining appar'atus used to admix the components of the composite layer.

The upper limit on the amount of heat-fusible polymer particles is 89 weight percent because of the requirement for at least 10 percent by weight of cellulose fibers and at least 1 percent by weight of a

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ft 755'-F-- -6- -7binder. The lower limit of 10 weight percent is mandated by a requirement for sufficient thermoplastic polymer to form a matrix which will hold together during preparation of the mat. The amount of heatfusible particles will vary depending upon whether incorporation of filler particles into the composite layer is also desirable. In general, however, the amount of heat-fusible particles is beneficially from to 83, desirably from 55 to 83 percent by weight of the composite layer.

If desired, the composite layer may also contain a particulate filler material in an amount of o from 5 to 80 percent by weight, based upon the combined S* 15 weight of filler material, cellulose fibers and heatfusible polymer.

Although the amount thereof which will provide satisfactory results may vary, any cellulosic fiber or 20 S 2 mixture of cellulose fibers may be used for purposes of the present invention. The cellulose fibers are 4 1 beneficially in the form of hardwood kraft pulp, *i4 softwood kraft pulp, softwood bisulfite pulp, thermomechanical pulp, chemithermomechanical pulp, u recycled paper and mixtures thereof. The cellulose fibers are desirably in the form of softwood kraft pulp.

Mixtures of noncellulosic fibers with cellulosic fibers are suitable for purposes of the t present invention and include those disclosed in U.S.

Patent Numbers 4,426,470 and 4,550,131. Particularly suitable fibrous materials for admixture with cellulose 35,755-F -7r: LI p 9* 9 ,B a a

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4.49r 4* 9 9 9 .9 SR I a pa 9: 99 al a 99 -8fibers are silicate mineral fibers, glass fibers, polyamide fibers, polyester fibers, and carbon fibers.

When desired, the composite layer may contain noncellulosic fibers in an amount of from 5 to percent by weight, based upon the combined weight of filler material, noncellulosic fibers, cellulose fibers and heat-fusible polymer.

Binder materials suitable for purposes of the present invention include those disclosed in U.S.

Patent Numbers 4,426,470 and 4,550,131. Particularly suitable binder materials are aqueous latexes or dispersions selected from a salt of a terpolymer of 15 styrene, butadiene and an a,p-ethylenically unsaturated carboxylic acid, a salt of an ethylene acrylic acid copolymer having an acrylic acid content of from 12 to percent by weight of copolymer solids, a natural rubber, a polyisoprene, a starch, and a copolymer of 20 ethylene and vinyl acetate. The binder is preferably a salt of an ethylene acrylic acid copolymer having an acrylic acid content of from 12 to 30 percent by weight of copolymer solids.

25 Satisfactory heat-fusible polymers include those disclosed in U.S. Patent Number 4,425,470 cited hereinabove. The heat-fusible polymer is beneficially lelected from polyethylene, chlorinated polyethylene, p)lypropylene, mixtures of polyethylene and polypropylene, and mixtures of polyethylene and polyvinyl chloride.

The composite layer is bonded to the wood product base layer by application of heat and pressure for a period of time sufficient to allow such bonding *9 35,755-F -8i- f -9to occur. Heating takes place at a temperature within a range of from 1290C to a temperature at which components of the wood product layer or the composite layer degrade. The temperature is suitably within a range of from 1290 to 204°C. Beneficial results, in terms of bonding, are obtained at a temperature of 163°C, a pressure of 1.38 megapascals and a time length of two minutes. The temperature, pressure and time length may vary depending upon the softening point, the melting temperature and the temperature at which the heat-fusible polymer degrades. By way of illustration, Bao satisfactory bonding is effected at a temperature of 163°C when the heat-fusible polymer is polyethylene and S 15 at a temperature of 177°C when the heat-fusible polymer D 15 orr. is polypropylene.

If the composite layer contains more than percent by weight of filler, satisfactory bonding is S 20 difficult, if not impossible, to obtain where the composite layer is in direct contact with the wood product base layer. Beneficial results are obtained, "however, if either an unfilled composite layer or a thermoplastic polymer film layer is disposed between the base layer and the filled composite layer. The heat-fusible polymer in the filled layer is desirably S. at least compatible with, and preferably the same as, the heat-fusible polymer in the unfilled layer of the thermoplastic polymer in the intermediate film layer.

The choice of wood product base layer is not particularly critical. As such, hardwood, softwood, plywood, partiole board, wafer board and the like may be used.

35,755-F -9- The wood product laminates of the present invention may be used in a variety of protective applications such as cupboard shelves and furniture drawers. They may also be used as concrete pouring forms as they provide a smooth surface and are reusable with minimal cleaning and no oiling between uses. The laminates may be cut with a saw or drilled substantially without delamination. Delamination is also insignificant, if it occurs at all, when fasteners such as screws or nails are driven through the laminate with a screwdriver or hammer as appropriate.

^The following examples are for pirposes of illustration only and are not to be construed as 1 limiting the scope of the present invention. Examples 1 of the present invention are designated by Arabic numerals and comparative examples are represented by alphabetic characters. All parts and percentages are I 20 by weight and all temperatures are in °C unless otherwise specified. The Canadian Standard Freeness t-t (Standard C. 1) (revised, April 1972) used herein i is prepared by the Physical and Chemical Standards Committee, Technical Section, Canadian Pulp Paper Association.

SI Example 1 Laminate Prepared With a Composite Layer Containing 10 Parts of Softwood Cellulose Fibers and 90 Parts of High Density Polyethylene S, a A composite containing 10 parts of bleached kraft softwood pulp, 90 parts of high density o polyethylene and three parts of an ethylene/acrylic acid oopolymer was prepared in several sequential steps. First, 100 grams of pulp were added to about 13 kilograms of water in a refining apparatus known as a 35,755-F

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After about 5 minutes of mixing, 120 grams of an aqueous dispersion (25 percent solids) of an ammonium salt of an ethylene/acrylic acid copolymer (acrylic acid content of 20 percent) commercially available from The Dow Chemical Company under the trade designation Primacor M 4983 were added over a period of 5 minutes while continuing the mixing. This was followed by addition of 900 grams of a high density polyethylene resin powder, commercially available from The Dow Chemical Company under the trade designation LP51.2, with continued stirring over a period of about 12 minutes. The resultant slurry was refined for a 15 further 20 minutes until a Canadian Standard Freeness of 250 milliliters (ml) was obtained. The pH of the slurry was then adjusted from 8.6 to 6.0 by addition of 20 grams of dilute (5 percent) acetic acid with continued mixing over a period of 5 minutes to 20 flocculate slurry solids. The solids were then dewatereci on a wire screen to form a coherent wet web which was dried at 105 0 C and atmospheric pressure on an Emerson speed dryer to form an opaque mat having visually uniform texture and a thickness cC about 3G micrometers.

Two layers of the mat were hot-pressed onto a major planar surface of a 250 mm x 250 mm x 6 mm thick piece of plywood at a temperature of 163'C and a pressure of 1.38 megapascals for a period of 2 minutes to provide a smooth, hydrophobic surface. The plywood was manufactured by MacMillan Bloedel Limited and designated as 6 mm, good one side, Douglas Fir, 3ply, suitable for exterior and, inter'ior use, bonded with phenol formaldehyde resin. The press was a Given

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Isr I It I I I It It It Using the same procedure, two layers of the mat S were hot-pressed onto a major planar surface of a 250 mm x 250 mm x 6 mm thick piece of particle board. The particle board was manufactured by MacMillan Bloedel Limited and designated as 6 mm particle board with the wood particles bonded with urea formaldehyde resin and suitable for interior use. After cooling the laminate to ambient temperature, a flat tip screwdriver (180 mm long with a 5 mm wide blade) was used in an attempt to separate the composite material from the underlying plywood or particle board surface. Although the metal blade cut the composite layer, only a small area of about 6 mm x 4 mm immediately adjacent the blade was removed. The remaining composite material remained firmly bonded to the uncrlying surface. In other words, the composite material layer did not delaminate as a single, contiguous layer.

Examples 2-7 Replication of Example 1 With Variations in Composition of the Composite Layer Save for changing the composition of the composite material layers, the procedures of Example 1 were duplicated. The composite layer compositions were as follows: Example 2 10 parts softwood kraft pulp, parts high density polyethylene and 80 parts of the ethylene/acrylic acid copolymer salt; Example 3 parts softwood kraft pulp, 85 parts high density polyethylene and 3 parts of the ethylene/acrylic acid copolymer salt; Example 4 25 parts softwood kraft pulp, 75 parts high density polyethylene and 1 part of the ethylene/acrylic acid copolymer salt; Example 5

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As in Example 1, a smooth, uniform surface was produced by hot-pressing. Also as in Example 1, the composite material could not be peeled off as a single,

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r contiguous layer from the underlying plywood (Examples i 15 2-6) or particle board surface (Examples 2-7).

From the data presented in Exaiples 1-7, it is clear that satisfactory laminates are prepared with cellulose fiber contents of from 10 to 50 parts, heatusible polymer contents of from 10 to 90 parts and 20 binder contents of from 1 to 80 parts.

S* Example 8 Bonding Temperature Variation Using the procedures of Example 1, composite mats containing 25 parts hardwood kraft pulp, 75 parts high density polyethylene and 3 parts of the ethylene/acrylic acid copolymer salt were prepared.

The procedure for hot-pressing two mats to a major planar surface of a piece of plywood was also followed except for varying the temperature to study the effect rM of temperature on bonding. The following temperatures t in oC were used: 1180, 1240, 129°, 1350, 140, 1460, 1520, 1570, 1900 and 204°. All temperatures save for 1180 and 1240 provided satisfactory bonding.

35,755-F -13- 0 -14- Examples 9-13 Variation of Pinder Using the procedures of Example 1, composite mats containing 25 parts softwood kraft pulp, 75 parts high density polyethylene and 3 parts of different binders were prepared and hot-pressed onto plywood and particle board surfaces. The following binders were Sused: Example 9 an experimental carboxylated styrene/butadiene latex available from The Dow Chemical Company under the trade designation XD 30570.3; Example 10 a natural rubber latex commercially available from 0* Goodyear Tire and Rubber Company under the trade designation Hartex 102; Example 11 a high-butadiene S* 15 content latex commercially available from Goodyear Tire and Rubber Company under the trade designation Pliolite" 5356; Example 12 a carboxylated styrene/ butadiene latex commercially available from The Dow Chemical Company under the trade designation DL 620; 20 and Example 13 a vinyl acetate latex commercially r available from National Starch Chemical Co. under the trade designation X-link

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2804. All binder materials S. provided the same results as obtained in Example 1 in terms of a strong bond between the composite material layer and the wood product layer.

S. The data presented in Examples 9-13 show that a variety of binder materials produce satisfactory results. Similar results are expected with other binder materials as well as with other composite variations, all of which are disclosed herein.

Examples 14-17 Variation of Cellulose Fiber Source 5 Using the procedures of Example 1, composite Smaterial mats were prepared and subjected to hot- 35,755-F -14pressing onto a plywood surface in order to evaluate different cellulose fibers. The compositions were as follows: Example 14 25 parts used newsprint (85/15 weight ratio of groundwood pulp and thermomechanical pulp), 75 parts high density polyethylene, 1.5 parts ethylene/acrylic acid copolymer and 3 parts of the styrene/butadiene latex used in Example 9; Example 15 parts sulfite softwood pulp, 75 parts high density polyethylene and 3 parts of the styrene/butadiene latex used in Example 12; Example 16 25 parts S'!r chemithermomechanical pulp, 75 parts high density polyethylene and 3 parts of the styrene/butadiene latex used in Example 9; and Example 17 35 parts t* 15 chemithermomechanical pulp, 65 parts high density polyethylene and 3 parts of the styrene/butadiene latex used in Example 12. The different cellulose materials provided the same results as obtained in Example 1 in terms of a strong bond between the composite material 20 layer and the wood product layer.

The data presented in Examples 14-17 show that S ra variety of cellulose materials produce satisfactory results. Similar results are expected with other cellulose materials as well as with other composite ,variations, all of which are disclosed herein.

Examples 18-22 Variation of Heat-Fusible Polymer 3 30 Using the procedures of Example 1, composite material mats were prepared and subjected to hotpressing onto a plywood surface in order to evaluate different heat-fusible polymers. The compositions were as follows: Example 18 25 parts softwood kraft pulp, parts chlorinated polyethylene, commercially available from The;Dow Chemical Company under the trade S35,755-F

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i t ,I -A ti.. ^Ie -16designation Tyrin T 0136, and 3 parts ethylene/acrylic acid copolymer salt; Example 19 25 parts softwood kraft pulp, 75 parts of a 50/50 blend of high density polyethylene and a polypropylene commercially available from Himont Inc. under the trade designation PF212PM, and 3 parts ethylene/acrylic acid copolymer salt; Example 20 identical to Example 19 save for using the styrene/butadiene latex of Example 9 as the binder; Example 21 25 parts softwood kraft pulp, 75 parts of the polypropylene used in Example 19 and 3 parts of the styrene/butadiene latex of Example 9; and Example 22 parts softwood kraft pulp, 75 parts of a 50/50 blend of high density polyethylene and a polyvinyl chloride 15 commercially available from Esso Chemical Canada under ;the trade designation ESSO 369, and 3 parts ethylene/acrylic acid copolymer salt.

The different heat-fusible polymers provided the same results as obtained in Example 1 in terms of a strong bond between the composite material layer and the wood product layer. In Example 21, heating at 163° Sdid not produce a suitable bond as the composite material layer could be peeled off with a screwdriver.

However, by increasing the temperature to 177 0 C, a bond comparable to that obtained in Example 1 was observed.

The data presented in Examples 18-22 show that a variety of heat-fusible polymers produce satisfactory results. As in Example 21, some variation in bonding conditions may be necessary to prepare an acceptable product. Similar results are expected with other heatfusible polymers as well as with other composite variations, all of which are disclosed herein.

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0 "0 In Example 23, a 0.03 mm layer of polypropylene S film fabricated from Himont PD943 resin, commercially available from Himont, Inc., was placed between one mat identical to that of Example 21 and a plywood surface.

Hot pressing took place as in Example 1, but at a temperature of 177C.

In Example 24, three different composite material layers were hot-pressed onto a plywood surface using the same conditions as in Example 1. The layer Sadjacent the plywood surface was identical to that used Sin Example 3. The middle layer was identical to that Sof Example 22. The top layer contained 25 parts softwood kraft pulp, 75 parts of the polyvinyl chloride used in Example 22 and 3 parts of the ethylene/acrylic S 20 acid salt.

In Example 25, a 0.07 mm layer of high density polyethylene film fabricated from resin designated HMW- HDPE 62013, commercially available from Dow Chemical Canada Inc. was placed between a plywood surface and two mats similar to that of Example 4 except for using 3 parts of the ethylene/acrylic acid salt rather than one. Hot pressirg took place as in Example 1.

In Example 26, a 0.05 mm layer of low density polyethylene film fabricated from resin designated LDPE 493 commercially available from Dow Chemical Canada SInc. was placed between a plywood surface and two mats identical to that of Example 8. Hot pressing took place as in Example 1.

35,755-F -17j 0 I Exmple26,a 005 m laer f lo desit t .1 -t 1 I 1- ''1 A L -18- In Example 27, a 0. 15 mm layer of linear low density polyethylene film fabricated from resin designated LLDPE 2045 commercially available from Dow Chemical Canada Inc. was placed between a plywood surface and two mats identical to that of Example 3.

Hot pressing took place as in Example 1.

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4444 4b 44 4 44 4, 4 44 The laminate structures of Examples 23-27 prcvided the ame results as obtained in Example 1 in 10 terms of a strong bond between the composit~e material layers and the wood product layer.

The data pre'sente-d in Examples 23-27 show that satisfactory results are obtained when thermoplastic film layers are interposed between the composite materials and the wood product surface. Similar results aro expected with other thermoplastic polymer film and composite material variations, all of which are disclosed herein.

Comparative Example A and Example 28 Improvembnt of Bonding Strength In Comparative Example A, two layers of a 25 composite material mat were prepared and subjected to hot-pressing onto a plywood surface in order to evaluate whether polyvinyl chloride is a suitable heatfusible polymer. The composition of the mat was parts softwood kraft pulp, 75 parts of the polyvinyl chloride used in Example 22 and 3 parts ethylene/acrylic acid copolymer salt. Although the composite layer had a smooth, hydrophobic surface, it did not adhere well to the plywood surface and could be off as a single, contiguous layer using a screwdriver.

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-19- In Example 28, a composite layer identical in composition to that of Example 8 was interposed between the composite layer of Comparative Example A and a plywood surface. Both layers were subjected to hotpressing onto the plywood surface. As in Example 1, the composite layers adhered strongly to the plywood surface and could not be peeled off as a single, contiguous layer from that surface.

10 From Comparative Example A and Ext. -le 28, it is aprirent that satisfactory laminates are prepared wherein a composite layer of the present invention is used as a tie layer for a different composite layer which does not bond strongly when applied directly to a plywood surface. Similar results are expected with other laminates of the present invention.

o, Comparative Examples B-E -Composites Which Exhibit Little or No Bonding Using the procedures of Example 1, composite material mats were prepared and subjected to hota" pressing onto a plywood surface in order to evaluate different composite layer compositions. The 2 compositions were as follows: Comparative Example B parts softwood k'aft pulp, 75 parts of the polyvinyl chloride of Comparative Example A, and 3 parts of a vinyl acetate latex, commercially available from National Starch under the trade designation X-Link 2804; Comparative Example C 50 parts softwood kraft pulp, 50 parts of the high density polyethylene of ig Example 1 and 3 parts ethylene/acrylic acid copolymer salt; Comparative Example D 60 parts thermomechanical pulp, 40 parts of the high density polyethylene of Example 1 and 3 parts of the carboxylated

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35,755-F -19- 7 I styrene/butadiene latex of Example 12; and Comparative Example E 75 parts softwood kraft pulp, 25 parts of the high density polyethylene of Example 1 and 3 parts ethylene/acrylic acid copolymer salt.

The composite layers of Comparative Examples B- E all provided smooth, hydrophobic surfaces. They did not, however, adhere well to the plywood surfaces as •they could be peeled off as a single contiguous layer 10 with a screwdriver.

The data presented in Comparative Examples B-E *highlight several points. First, a simple change in a binder material does not improve bonding (Comparative Example B versus Comparative Example Second, the choice of cellulose fiber is quite important (Example 7 i versus Comparative Example Third, an excessive a' amount of cellulose fiber adversely affects interlayer bonding (Comparative Examples D and Similar 20 S 2. 0 results are expected with other variations which are outside the scope of the present invention.

S Comparative Example F and Example 29 Filled Composite Layer In Comparative Example F, two layers of a composite material mat were prepared and subjected to hot-pressing onto a plywood surface in order to evaluate whether a filled composite mat provides a satisfactory laminate structure. The composition of the mat was 20 parts softwood kraft pulp, 40 parts of the high density polyethylene used in Example 1, parts calcium carbonate, 4 parts titanium dioxide, and 3 parts ethylene/acrylic acid copolymer salt. Although the composite layer had a, smooth, hydrophobic surface, 35,755-F a 1 1 S-21it did not adhere well to the plywood surface and could be peeled off as a single, contiguous layer using a screwdriver.

In Example 29, a composite layer identical in composition to that of Example 8 was interposed between the composite layer of Comparative Example F and a plywood surface. Both layers were subjected to hotpressing onto the plywood surface. As in Example 1, 10 the composite layers adhered strongly to the plywood surface and could not be peeled off as a single, t V, contiguous layer from that surface.

SComparative Example G and Example 31 Filled Composite Layer t o n Comparative Example G, two layers of a |composite material mat were prepared and suLjected to hot-pressing onto a plywood surface in order to 20 evaluate whether a filled composite mat provides a satisfactory laminate structure. The composition of the mat was 20 parts softwood kraft pulp, 20 parts of "the high density polyethylene used in Example 1, Sparts calcium carbonate, and 3 parts of the 25 carboxylated styrene/butadiene latex of Example 12.

Although the composite layer had a smooth, hydrophobic surface, it did not adhere well to the plywood surface and could be peeled off as a single, contiguous layer using a screwdriver.

In Example 30, a composite layer identical in composition to that of Example 4 was interposed between the composite layer of Comparative Example G and a plywood surface. Both layers were subjected to hotpressing onto the plywood surface. As in Example 29, 35,755-F 21 i I 'Se -22the composite layers adhered strongly to the plywood surface and could not be peeled off as a single, contiguous layer from that surface.

Comparative Example H and Example 31 Filled Composite Layer In Comparative Example H, two layers of a composite material mat were prepared and subjected to 10 hot-pressing onto a plywood surface in order to evaluate whether a filled composite mat provides a S'satisfactory laminate structure. The composition of the mat was 20 parts softwood kraft pulp, 20 parts of ,i the high density polyethylene used in Example 1, parts aluminum trihydrate, and 3 parts ethylene/acrylio acid copolymer salt. Although the composite layer had a smooth, hydrophobic surface, it did not adhere well to the plywood surface and could be peeled off as a single, contiguous layer using a screwdriver.

In Example 31, a composite layer identical in Scomposition to that of Example 8 was interposed between •the composite layer of Comparative Example H and a plywood surface. Both layers were subjected to hot- 25 2 pressing onto the plywood surface. As in Examples 29 and 30, the composite layers adhered strongly to the plywood surface and could not be peeled off as a single, contiguous layer from that surface.

Comparative Example I and Example 32 Filled Composite Layer I In Comparative Example I, two layers of a i composite material mat were prepared and subjected to hot-pressing onto a plywood surface in order to evaluate whether a filled composite mat provides a 35,755-F -22c 1 -23satisfactory laminate structure. The composition of the mat was 20 parts softwood kraft pulp, 20 parts of the high density polyethylene used in Example 1, parts magnesium hydroxide, and 3 parts ethylene/acrylic acid copolymer salt. Although the composite layer had a smooth, hydrophobic surface, it did not adhere well to the plywood surface and could be peeled off as a single, contiguous layer using a screwdriver.

10 In Example 32, a composite layer identical in composition to that of Example 8 was iaterposed between the composite layer of Comparative Example I and a t plywood surface, Both layers were subjected to hotpressing onto the plywood surface. As in Examples 29- 31, the composite layers adhered strongly to the plywood surface and could not be peeled off as a single, contiguous layer from that surface.

From Comparative Examples F-I and Examples 29- ,1 20 J 32, it is apparent that satisfactory minates are prepared wherein a composite layer of the present invention is used as a tie layer for a different SI composite layer which does not bond strongly when i 25 applied directly to a plywood surface. Similar results are expected with other laminates of the present S invention.

Example 33 Filled Composite Layer With Intermediate Linear Low Density Polyethylene Film Layer In Example 33, a single layer of the filled composite material mat of Comparative Example I was placed on top of a 0.07 mm thick layer of linear low density polyethylene film. The combined layers were subjected to hot-pressing onto a plywood surface in I35,755-F -23- -24order to evaluate wI-~her a polymer film layer could be used to bond a filled composite layer to a wooden surface thereby providing a satisfactory laminate structure. The film was prepared from the same resin as the film layer of Example 27. The resulting laminate structure had a smooth hydrophobic surface and, as in Example 1, the composite layer could not be peeled from the plywood surface as a single contiguous layer.

1 *S Example 34 Filled Composite Layer With Intermediate Low Densty Polyethylene Film Layer In Example 34, a single layer of the filled composite material mat of Comparative Example H was placed on top of a 0.03 mm thick layer of low density o, polyethylene film. The combined layers were subjected o a to hot-pressing onto a plywood surface in order to evaluate whether a polymer film layer could be used to 20 S 20 bond a filled oomposite layer to a wooden surface thereby providing a satisfactory laminate structure.

The film was prepared from the same resin as the film layer of Example 26. The resulting laminate structure 25 had a smooth hydrophobic surface and, as in Example 1, the composite layer ould not be peeled from the plywood surface as a kingle contiguous layer.

Example 35 Filled Composite Layer With Intermediate High Density Polyethylene Film Layer In Example 35, a single layer of the filled composite material mat of Comparative Example G was p. placed on top of a 0.07 mm thick layer of high density polyethylene film. The combined layers were subjected to hot-pressing onto a plywood surface in order to 35,755-F -24- -7 evaluate whether a polymer film layer could be used to bond a filled composite layer to a wooden surface thereby providing a satisfactory laminate structure.

The film was prepared from the same resin as the film layer of Example 25. The resulting laminate structure had a smooth hydrophobic surface and, as in Example 1, the composite layer could not be peeled from the plywood surface as a single contiguous layer.

10 From Examples 33-35, it is apparent that satisfactory laminates are prepared wherein a polymer film layer is used as a tie layer for a filled composite layer which does not bond strongly when applied directly to a plywood surface. Similar results are 15 expected with other laminates of the present invention.

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Claims (9)

1. A laminate comprising a base layer of a wood product and at least one dry mat composite layer bonded thereto by heat and pressure, the ia composite layer comprising, based on layer weight, from 10 to 50 fi percent by weight of cellulose fibers, from 10 to 89 percent by weight fi of a solid heat-fusible polymer in particulate form, and from I to percent by weight of a binder, the bonding between the composite layer se being sufficiently strong to preclude removal of the composite layer as a single, contiguous sheet.

2. The laminate of Claim 1, wherein the cellulose fibers are co hardwood kraft pulp, softwood kraft pulp, softwood bisulfite pulp, pr thermomechanical pulp, chemithermomechanical pulp, recycled paper, or wi mixtures thereof.

3. The laminate of Claim I or Claim 2, including at least one ar intermediate thermoplastic polymer film layer disposed between the base layer and the composite layer.

4. The laminate of any one Qof Claims 1 to 3, wherein the composite layer contains a particulate filler material in an amount of from 5 to 80 E percent by weight, based on the combined weight of the filler material, cellulose fibers and heat-fusible polymer. The laminate of Claim 4, wherein the filler material is selected from calcium carbonate, aluminum trihydrate, magnesium hydroxide, silicon dioxide, titanium dioxide, clay, silicates, carbon black, or mixtures thereof.

6. The laminate of any one of Claims 1 to 5, wherein the binder is an aqueous dispersion selected from a salt of a terpolymer of styrene, butadiene and an a,p-ethylenically unsaturated carboxylic acid, a salt of an ethylene acrylic acid copolymer having an acrylic acid content of from 12 to 30 percent by weight of copolymer solids, a natural rubber, a polyisoprene, a starch, and a copolymer of ethylene and vinyl acetate.

7. The laminate of Iny one of Claims 1 to 6, wherein the binder is present in an amount of from 1 to 6 percent by weight of the composite layer.

8. The laminate of any one of Claims 1 to 7, wherein the heat-fusible polymer is selected from polyethylene, chlorinated S/TMR/ TMR/4229T ^B .s iVm T 11 1 1 B 1 p ^>^tiw~~ii~ii n 1 1 1 i l S P 27 polyethylene, polypropylene, mixtures of polyethylene and polypropylene, and mixtures of polyethylene and polyvlnyl chloride.

9. The laminate of any one of Claims 1 to 8, wherein the composite layer further comprises from 5 to 40 percent by weight of noncellulosic fibers, based on the combined weight of filler material, noncellulosic fibers, cellulose fibers and heat-fusible polymer.

19. The laminate of Claim 9, wherein the noncellulosic fibers are selected from silicate mineral fibers, glass fibers, polyamide fibers, polyester fibers, carbon fibers, or mixtures thereof. 11. The laminate of any one of Claims 1 to 10 including a filled composite layer superimposed on, and bonded by application of heat and pressure, to the composite layer, said filled composite layer being filled with a particulate filler material in an amount of from 5 to 80 percent by weight, based on the combined weight of filler material, cellulose fibers and heat-fusible polymer. 12. A laminate comprising a base layer of a wood product and at least one dry mat composite layer bonded thereto by heat and pressure, substantially as hereinbefore described with reference to any one of the Examples. DATED this SEVENTH day of DECEMBER 1989 The Dow Chemical Company Patent Attorneys for the Applicant SPRUSON FERGUSON A I I TMR/4229T O 1 i l i i 1 ;A