Coated sheet material for use in making decorative laminates

Disclosed is a coated sheet material comprising a release medium having thereon a gluable coating for use in making a decorative heat-and-pressure consolidated laminate. The gluable coating is transferred during the consolidation step from the release medium to the back side of the laminate, and the laminate can then be glued to a reinforcing substrate with conventional glues and without sanding the back of the laminate. The transferable gluable coating comprises a linear copolymer of (A) maleic anhydride or maleic acid or maleic acid salt and (B) ethylene or a vinyl monomer having a side chain of an aliphatic group with up to four carbon atoms or an alkoxy group with up to four carbon atoms.

BACKGROUND OF THE INVENTION 
Field of the Invention 
In making decorative laminates, a plurality of sheets impregnated with a 
thermosetting resin are assembled in a stacked, superimposed relationship 
with a decorative sheet placed on top. The assembly is placed between 
platens and then heat-and-pressure consolidated. 
Generally, more than one laminate is formed at one time by inserting a 
plurality of assembled sheets in a stack with each assembly being 
separated by a release sheet which allows the individual laminates to be 
separated after consolidation. The laminates so formed are then bonded to 
a reinforcing substrate, such as plywood, particle board or the like, by 
the use of adhesives such as contact adhesives, urea-formaldehyde, white 
glues (polyvinyl acetate emulsions) hot melts, phenolic or 
resorcinol-formaldehyde epoxy, coal tar, animal glues, and the like. The 
glues vary in their cost and reliability. A very commonly used glue in the 
industry is a polyvinyl acetate emulsion sold under the name Wood-Lok No. 
40-0536. This glue is inexpensive and reliable, but is not versatile in 
the variety of laminating surfaces it will adhere to. 
In the typical operation where polyvinyl acetate glues, as well as many of 
the other glues, are used, the laminate is first sanded on its back 
surface before it is glued to its supporting substrate. This is because 
the conventional glues will not directly adhere to the phenolic 
impregnated back sheet of the laminate. In addition, some of the release 
mediums used to separate laminates during consolidation permit some of the 
release material to transfer to the back surface of the laminate and 
reduce the gluability of the laminate to the reinforcing substrate. By 
back surface, it is meant the exposed flat surface of the laminate which 
is furthermost from the decorative sheet and which is to be glued to the 
reinforcing substrate. 
The sanding operation is an expensive step in the process and adds to the 
cost of the product. The step can also be responsible for increased waste 
of the laminated material. Since the laminates are relatively inflexible 
after the resins contained therein have been thermoset during the 
consolidation process, the thin laminates are particularly susceptible to 
damage during the sanding step due to their brittleness. 
It may be possible to eliminate the sanding step by using certain glues 
which have the ability to adhere to the phenolic impregnated back sheet. 
However, such glues are expensive and have not been readily accepted by 
manufacturers of reinforced laminates. Each manufacturer has learned 
through years of experience that he can rely upon certain glues. When 
considering his potential liability for laminates that separate from their 
reinforcing substrate after they have been fabricated into expensive 
furniture, cabinets and the like, it is understandable why the 
manufacturers are reluctant to change glues. Accordingly, the prevailing 
practice in the industry continues to be sanding the back surface of the 
laminate and using the well tested polyvinyl acetate glues. 
There are existing techniques which are designed to provide a gluable back 
surface for the laminate without sanding. For example, U.S. Pat. No. Re. 
27, 644 to Kelly and Grosheim discloses a laminate coated on its back 
surface with a polyvinyl acetate composition. However, laminates produced 
in accordance with this technique have the disadvantage of not being 
easily consolidated in contact with one another in a stack without 
adhering to one another during the consolidation process. 
U.S. Patent Application No. 600,225, filed July 30, 1975 in the names of 
William A. Hosmer and William M. Bowler, discloses a gluable backing sheet 
which becomes the back surface of a decorative laminate during 
consolidation and provides a surface which is gluable to reinforcing 
substrates with a variety of the most commonly used glues. In addition, 
the Hosmer/Bowler invention provides the ability to consolidate laminates 
in back-to-back arrangement by providing a pair of backing sheets placed 
together between laminates, with each backing sheet ahdering to a 
different laminate. The backing sheet is coated with a composition of an 
inert filler (such as clay), a non-thermoplastic adhesive (such as 
proteinaceous adhesives) and a water-soluble, thermosetting resin selected 
from the class consisting of urea-formaldehyde resin condensates and 
melamine-formaldehyde resin condensates. A disadvantage of the 
Hosmer/Bowler invention is that two separate coated backing sheets are 
required when consolidating laminates in back-to-back configuration. 
U.S. Pat. No. 4,030,955 to Antonio and Uhl, discloses a transferable, 
gluable coating which adheres to the back surfaces of the decorative 
laminates during the consolidation step and provides a gluable surface 
which can be adhered to a reinforcing substrate without sanding the back 
surface of the laminate. The gluable layer is first coated on both sides 
of a release film of polypropylene and placed between back-to-back 
laminate assemblies. The coating then transfers to the laminate during 
consolidation. The gluable coating material employed is chosen from 
polyvinyl alcohol, animal glue and starch. A disadvantage of this 
invention is that the gluable coatings must be transferred from only 
particular release mediums, such as polypropylene sheets. If the gluable 
coating of Antonio/Uhl is transferred from a paper sheet coated with a 
release material, which is a particularly satisfactory and inexpensive 
release medium for separating laminates during consolidation, the 
gluability of the coating can be seriously impaired. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a decorative laminate with a 
gluable coating on its back surface suitable for gluing the decorative 
laminate to a reinforcing substrate with the most commonly employed glues 
and without first sanding the back surface of the laminate. 
It is a further object of the invention to provide a coated sheet material 
comprising a release medium having coated thereon a gluable coating which 
will transfer from the release medium to the back surface of a decorative 
laminate during the consolidation step. 
It is yet a further object of the invention to provide a gluable coating 
which can be transferred satisfactorily to the back surface of a 
decorative laminate during consolidation from a release medium provided by 
a paper sheet coated with a release material. 
And it is a further object of the invention to provide a coated sheet 
material which can be used to separate decorative laminates when they are 
being consolidated in back-to-back configuration. 
These and other objects are accomplished by the products and methods of the 
invention which feature a transferable, gluable coating comprising a 
linear copolymer of (A) maleic anhydride or maleic acid or maleic acid 
salt and (B) ethylene, or a vinyl monomer having a side chain of either an 
aliphatic group with up to four carbon atoms or an alkoxy group with up to 
four carbon atoms. 
The invention is a coated sheet material comprising a release medium which 
is coated on at least one side with the featured transferable, gluable 
coating. The invention is also the method of transferring the featured 
gluable coating to the back surface of a laminate during the laminate 
consolidation step. The invention is also a decorative heat-and-pressure 
consolidated laminate having on its back surface the featured gluable 
coating. The invention is also the method of gluing the decorative 
laminate with the featured gluable coating to a reinforcing substrate. And 
the invention is also a reinforced decorative laminate in which the 
featured gluable coating provides a glue line between the laminate and the 
glue which adheres the laminate to the reinforcing substrate. Preferred 
embodiments of the invention are set forth and described in the 
Description of the Preferred Embodiments and in the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The following examples illustrate the present invention. Examples 1-7 are 
actual examples of the present invention, and Examples 8-10 are examples 
of the prior art included for comparative purposes. 
EXAMPLE 1 
A release medium was prepared from a base paper made from highly refined 
long fibers and having a basis weight of about 57 lbs. per ream. 
(Throughout this specification the term "ream" shall refer to 3300 square 
feet.) The base paper was surface sized with a conventional poly(vinyl 
alcohol) and starch composition and then calendered for smoothness. A 
release coating was prepared by mixing 100 parts (by dry weight) of a 
copolymer of 1-octadecene and amleic anhydride and 32 active parts of 
potassium hydroxide with sufficient water to provide 15% solids. The 
copolymer was provided by Gulf Oil Corporation's PA-18 (a linear, low 
molecular weight 1:1 copolymer with the following properties: melting 
range-90.degree.-101.degree. C.; acid no. 321; molecular weight-1300; 
specific gravity 0.889; inherent viscosity 0.081, based on 5.0 g./dl. 
acetone at 77.degree. F.) The coating was cooked at 190.degree. F. for 
1/2-1 hour to form a clear solution and then was coated on both sides of 
the base paper with an air knife and dried. The coat weight on each side 
was 11/2-2 lbs. per ream. 
A transferable, gluable coating formulation of the invention was prepared 
as follows. 100 parts (by dry weight) of a copolymer of ethylene and 
maleic anhydride were mixed with 121/2 parts of Calgon (sodium 
hexametaphosphate, used as a wetting agent) and sufficient water to 
provide 10% solids. The copolymer was provided by Monsanto's EMA-11 (a 
linear 1:1 copolymer with the following properties: molecular 
weight-8,000; viscosity of 2% solution-2.0 cps.; softening 
point-170.degree. C.; melting point-235.degree. C.; bulk density-20 
lbs./ft..sup.3 ; pH of 1% solution-2.3). The coating mixture was cooked at 
190.degree. F. for 1/2-1 hour to form a clear solution and then coated 
with an air knife coater on both sides of the release medium described 
above and dried. The coat weight on each side was 3 lbs. per ream. 
The coated sheet material was then employed and tested in the following 
manner. A decorative, heat and pressure consolidated laminate was prepared 
by assembling in the following order, one decorative sheet which had 
previously been saturated with melamineformaldehyde resin, three sheets of 
corestock which had previously been saturated with a phenolic resin, and 
the coated sheet material described immediately above. Two such laminates 
were pressed simultaneously in back-to-back configuration with a single 
piece of the coated sheet material separating the two laminates, and with 
each of the decorative sheets in contact with a caul plate. Between each 
of the caul plates and the pess platens, there was inserted a sheet of 
unimpregnated caul stock, which was merely intended to even pressure 
distribution over the surfaces of the laminates being pressed. The 
laminates were pressed for 20 minutes at 280.degree. F. and at a pressure 
of 1200 lbs. per square inch to consolidate them, and then the press was 
cooled for about five minutes in order to allow the caul plates to 
approach room temperature. Upon removal of the laminates from the press, 
they were easily separated from the coated sheet material, and the gluable 
layer on each side of the coated sheet material was found to have 
substantially completely transferred to the back surface of its respective 
laminate. 
Each of the resulting laminates were then subsequently glued to a 
reinforcing substrate in the form of a 3/8 inch thick particle board to 
which there had previously been applied a very commonly used polyvinyl 
acetate glue (National Starch's Wood-Lok No. 40-0536) at a rate of from 
about 10 to about 20 lbs. of glue per 1000 square feet of particle board. 
The amount of glue applied was intended to be sufficient to thoroughly and 
uniformly coat the entire surface of the particle board to which the 
laminates were being glued, yet minimize the "squeeze out" of the glue 
during the gluing step. Each of the laminates were pressed onto the 
particle board with the back side down (the side with the gluable layer), 
and then placed in a press at 50-75 lbs. per square inch pressure and at 
room temperature for approximately one hour. Upon removal from the press, 
the glued samples were then allowed to further set for an additional 24 
hours, during which time the faces of each of the samples were scarified 
with a saw the full length of the face at one-inch intervals and down 
through the thickness of the laminate and into the particle board for 
testing purposes. 
The testing of the samples involves pulling a strip of the laminate from 
the surface of the particle board and then observing the amount of wood 
particles which separated from the particle board and adhered to the back 
of the stripped laminate (the greater the number of particles, the better 
the bond). Wood particles adhering to the back of the stripped laminate 
were found to cover about 10% of the surface of the laminate. This amount 
is considered satisfactory for a test made after only 24 hours. 
EXAMPLE 2 
A coated sheet material like that of Example 1 was prepared, except that 
the particular copolymer in the gluable coating of Example 1 was replaced 
with another ethylene maleic anhydride copolymer, Monsanto's EMA-31 (which 
differs from EMA-11 by having a molecular weight of 100,000 and a 
viscosity of 7.0 cps. for a 2% solution). The coat weight on each side of 
the coated sheet material of Example 2 was 4 lbs. per ream. The coated 
sheet material was employed in the same manner as in Example 1. Again the 
gluable layer substantially completely transferred from the release medium 
to the back surface of the consolidated laminate. The laminate was tested 
in the same manner as in Example 1, and wood particles adhering to the 
back of the stripped laminate were found to cover 40%-90% of the surface 
of the laminate for a number of samples. 
EXAMPLE 3 
A coated sheet material like that of Example 1 was prepared, except that 
the copolymer in the gluable coating of Example 1 was replaced with a 
copolymer of maleic acid salt and a vinyl monomer having a side chain of 
an aliphatic group with four carbon atoms, Gulf Oil Corporation's PA-6 (a 
linear, low molecular weight 1:1 copolymer with the following properties: 
melting range 143.degree.-166.degree. C.; equivalent acid value-617; 
specific gravity 0.92; inherent viscosity 0.098 based on 5.0 g./dl. 
acetone at 77.degree. F.; and molecular weight of 5000). The copolymer was 
100% neutralized with potassium hydroxide, and the coat weight on each 
side of the coated sheet material was 2 lbs. per ream. The coated sheet 
material was employed in the same manner as in Example 1. Again the 
gluable layer substantially completely transferred from the release medium 
to the back surface of the consolidated laminate. The laminate was tested 
in the same manner as in Example 1, and wood particles adhering to the 
back of the stripped laminate were found to cover 5-10% of the surface of 
the laminate. This amount is considered satisfactory for a test made after 
only 24 hours. 
EXAMPLE 4 
A coated sheet material like that of Example 1 was prepared, except that 
the copolymer in the gluable coating was replaced with a copolymer of 
maleic anhydride and a vinyl monomer having a side chain of an alkoxy 
group with one carbon atom, G.A.F.'s GANTREZ AN-119 (a linear poly(methyl 
vinyl ether/maleic anhydride) having the following properties: low 
molecular weight; coefficient of viscosity-0.1-0.5 as determined on a 
solution of 1 gm. in 100 ml.. of MEK at 25.degree. C.). The coat weight on 
each side of the coated sheet material was 5 lbs. per ream. The coated 
sheet material was employed in the same manner as in Example 1. Again the 
gluable layer substantially completely transferred from the release medium 
to the back surface of the consolidated laminate. The laminate was tested 
in the same manner as in Example 1, and wood particles adhering to the 
back of the stripped laminate were found to cover 10% of the surface of 
the laminate. 
EXAMPLE 5 
A coated sheet material like that of Example 1 was prepared, except that 
the copolymer in the gluable coating was replaced with a copolymer of 
maleic acid and a vinyl monomer having a side chain of an alkoxy group 
with one carbon atom, G.A.F.'s GANTREZ S-95 (hydrolyzed low molecular 
weight poly(methyl vinyl ether/maleic acid). The coat weight on each side 
of the coated sheet material was 4 lbs. per ream. The coated sheet 
material was employed in the same manner as in Example 1. Again the 
gluable layer substantially completely transferred from the release medium 
to the back surface of the consolidated laminate. The laminate was tested 
in the same manner as in Example 1, and wood particles adhering to the 
back of the stripped laminate were found to cover 40%-70% of the surface 
of the laminate for a number of samples. 
EXAMPLE 6 
A coated sheet material like that of Example 2 was prepared, except that 
the release medium was provided by a 1 mil thick polypropylene sheet and 
the transferable, gluable coating was applied to the sheet by rod drawdown 
to result in a dried coating weight on each side of from 4 to 5 lbs. per 
ream. The coated sheet material was employed in the same manner as in 
Example 1. Again the gluable layer substantially completely transferred 
from the release medium to the back surface of the consolidated laminate. 
The laminate was tested in the same manner as in Example 1, and wood 
particles adhering to the back of the stripped laminate were found to 
cover 60% of the surface of the laminate. 
EXAMPLE 7 
All of the steps of Example 2 were repeated, except that the laminate was 
glued to a reinforcing particle board with Borden's Cascorez WB-732 
polyvinyl acetate glue. (This glue is less commonly used than the Wood-Lok 
glue, but is more versatile in the variety of surfaces it will adhere to.) 
Wood particles adhering to the back of the stripped laminate were found to 
cover 50% of the surface of the laminate. 
EXAMPLE 8 
A commercially available sheet of the type disclosed in U.S. Pat. No. 
4,030,955 to Antonio and Uhl and having a gluable coating of polyvinyl 
alcohol coated on a 1 mil thick polypropylene sheet was used to 
consolidate a laminate in the manner of the previous examples. The 
laminate was glued to a reinforcing substrate and tested in the manner of 
Example 7, and wood particles adhering to the back of the stripped 
laminate were found to cover 40% of the surface of the laminate. 
EXAMPLE 9 
A coated sheet material similar to that of Example 8 was prepared by 
coating polyvinyl alcohol (DuPont's Elvanol 51-05, low molecular weight 
resin, with viscosity of 4-6 cp. for a 4% aqueous solution at 20.degree. 
C. determined by Hoeppler falling ball method, 87.7-89.7% hydrolysis, and 
pH of 5.0-7.0) on the same release medium employed in Examples 1-5 and 7. 
The coat weight on each side of the release medium was 15 lbs. per ream, 
chosen to simulate the coat weight on the commercially available sheet of 
Example 8. The coated sheet material was used in forming a consolidated 
laminate and tested as in Example 8. However, essentially no wood 
particles were found on the laminate surface after stripping, indicating 
that the polyvinyl alcohol coating is unsuitable as a gluable layer for 
the most commonly used glues when the coating has been transferred from a 
release material on the surface of paper. 
EXAMPLE 10 
A coated sheet material like that of Example 9 was prepared, except the 
release medium was provided by a 1 mil thick polypropylene sheet. The 
coated sheet material was used in forming a consolidated laminate and 
tested as in Example 9, and wood particles adhering to the back of the 
stripped laminate were found to cover 70% of the surface of the laminate. 
In order to determine how well a laminate is secured to a reinforcing 
substrate, the above-described stripping test is performed at various 
times after glueing and after subjecting the reinforced laminate to 
various conditions. For example, the reinforced laminate may be tested 
after 4 hours, after 24 hours, or after several days, or it may be tested 
after being subjected to a freeze and/or heat cycle. It has been found 
that a good indication of the future performance can be obtained from the 
24 hour test employed in the preceding examples. A finding of any 
significant wood fiber coverage on the stripped laminate at 24 hours 
indicates a successful embodiment, since the performance level will 
usually continue to improve with time. For example, 10% coverage or more 
is considered satisfactory. Even the 5%-10% coverage of Example 3 was 
satisfactory, since further tests of this embodiment showed significantly 
better results. 
The gluable coating of the invention can be coated on only one side of the 
release medium, but preferably it is coated on both sides. Coating on both 
sides permits the coated sheet material to be used in consolidating two 
laminates together in back-to-back configuration. It should be noted here 
that the release medium after the gluable coating has been transferred can 
generally be used as a conventional separator sheet to accommodate 
back-to-back consolidation of two laminates in the manner of the prior 
art. However, the laminates consolidated in this manner will not have a 
gluable layer and will probably have to be sanded before gluing them to 
reinforcing substrates. 
The release medium can be provided by a variety of materials, such as the 
two disclosed in the examples. Coated release paper is the most desirable 
because of its low cost. A number of other conventional release materials 
coated on paper were tried, and most were found satisfactory. It is 
important, however, that the base paper be properly prepared. Tests 
conducted on uncalendered paper and on excessively porous paper with 
otherwise satisfactory release materials on their surfaces indicated that 
they were unsatisfactory in their ability to transfer the gluable coating 
to the laminate. Thus, the same design considerations normally attendant 
with manufacturing any quality release papers also applies to the release 
medium employed in the present invention. It is easily within the 
capability of one having ordinary skill in making release papers to 
provide a satisfactory release medium for use in the present invention. 
The most preferred release medium is the one used in Examples 1-5 and 7, 
the copolymer of 1-octadecene and maleic anhydride coated on paper. This 
material is one of the most inexpensive and satisfactorily performing 
release mediums. 
The preferred gluable coating material is the copolymer of maleic anhydride 
and ethylene, particularly the higher viscosity EMA-31 of Example 2. 
However, cross-linked varieties of maleic anhydride and ethylene were 
found to be unsatisfactory, and only the linear copolymers seem to be 
satisfactory. 
The useful copolymers include those in the form of maleic anhydride, those 
hydrolyzed to maleic acid form, and those which are neutralized to the 
maleic acid salt form. Where a vinyl monomer is part of the copolymer the 
length of the side chain affects its ability to provide satisfactory 
gluability. Although varieties having all potential chain lengths were not 
tested, those tested in addition to the examples indicate that the 
aliphatic or alkoxy groups should not have more than 4 carbon atoms. The 
amount of the gluable coating to be attached to the laminate is not 
narrowly critical, but tests indicate that an amount of from about 1/2 lb. 
to 7 lbs. per ream is preferred. 
Having now described the preferred embodiments, variations within the scope 
of the invention will be obvious to those skilled in the art.