US 3764645 A
A method of press-molding sheet-coated articles especially of a platelike shape from a mixture of comminuted fibrous materials and a thermosetting binder by impressing conical or similar recesses in the normally lower side of the material for increasing especially during the hot-molding operation the rate of compression of the material within the marginal areas and especially the corner areas of the fibrous body of the article so as to prevent any shrinkage of the material while it is setting and thereby to insure that the covering sheet material will be firmly bonded to the fibrous body especially within these areas. The projections on the molding die for impressing the recesses also act as gripping means to prevent the shrinking of the material.
Description (OCR text may contain errors)
United States Patent Munk Oct. 9, 1973 METHOD OF MOLDING COATED 3,373,233 3/1968 Rondum 264/112 ARTICLES OF FIBROUS MATERIALS FOREIGN PATENTS OR APPLICATIONS  Inventor: Edmund E. Munk, Oberstenfeld, 1,255,300 H967 Germany Germany  Assignee: Furnier-und Sperrholzwerk J. F. Primary R0bert F White Werz Jr. K.G. Assistant Examiner-J. R. Hall Werzalit-Pressholzwerk Attorney-Michael S. Striker Oberstenfeld, Stuttgart, Germany Filed: May 3, 1971 [5 ABSTRACT Appl. No.: 139,535
Related U.S. Application Data  Foreign Application Priority Data May 2, 1968 Germany P 17 03 323.1
 U.S. Cl. 264/112  Int. Cl B29 5/04  Field of Search 264/112, 122
 References Cited UNITED STATES PATENTS 3,439,081 4/1969 Enderlein 264/112 llIll/llI/II/IIIIII/II/I/I/IIII/fl/ A method of press-molding sheet-coated articles especially of a platelike shape from a mixture of comminuted fibrous materials and a thermosetting binder by impressing conical or similar recesses in the normally lower side of the material for increasing especially during the hot-molding operation the rate of compression of the material within the marginal areas and especially the comer areas of the fibrous body of the article so as to prevent any shrinkage of the material while it is setting and thereby to insure that the covering sheet material will be firmly bonded to the fibrous body especially within these areas. The projections on the molding die for impressing the recesses also act as gripping means to prevent the shrinking of the material.
9 Claims, 5 Drawing Figures PATENTED 9|973' 3.784545 H6 20 & i b\\\\\\\\\\\\\ ATTORNE METHOD OF MOLDING COATED ARTICLES OF FIBROUS MATERIALS CROSS-REFERENCE TO RELATED APPLICATIONS The present application is a continuation-in-part application of the copending application Ser. No. 820,809, filed May 1, 1969 and now abandoned.
BACKGROUND OF THE INVENTION The present invention relates to a method of producing molded articles which may have planar or uneven surfaces and angular, rounded or specially-shaped projecting edges and are made by application of heat and pressure to a mixture of comminuted organic fibrous materials, for example, wood chips, with a hot-setting binder and are coated with a thin decorative sheet material.
More particularly, the invention relates to improvements in the method as disclosed by the present applicant in the patent granted in the Federal Republic of Germany, No. 1,255,300, and also in corresponding patents granted in numerous other countries.
In this known method which is generally carried out in two steps, a blank of substantially the same shape as, but a slightly larger size than the finally molded article, is first produced by cold-molding, and in a subsequent hot-molding operation this blank is further compressed to its final shape and size, the coating material is molded thereon, and the binder is set completely.
ln order to prevent the molded body as much as possible from shrinking during the setting of the molding mixture in the final hot-molding operation in which the thin sheet material is also bonded to the outer surfaces of the molded body, since such shrinkage would also cause the covering sheet material to be unequally and insufficiently bonded together with the molded body, the known method as disclosed in the mentioned German patent provides that the die for molding the normally lower side of the article is provided with projecting ridges for impressing continuous or interrupted grooves into the molding material which preferably extend parallel to and at a short distance from the edges of the molded body or from one or more projections on the other side of the body. These grooves are usually impressed during the hot-molding operation, although they may also be partly premolded in the cold-molded blank. These projecting ridges on the die are designed so that by molding the grooves they cause an additional compression of the material near the edges of the molded body and, if desired, also near a projection on the normal plane of this body, and thereby prevent any substantial shrinkage of the molding material while it is setting, especially with respect to the covering-sheet material, by insuring that the back pressure'which has to be exerted upon the outer surface of the sheet material to bond the same to the molded body will be suffi-, cient at all points and especially near the edges and projections of the body. Aside from effecting such additional compression, the ridges on the die also have the function of gripping the material while it is setting so that also for this reason no substantial shrinking can occur.
la the mentioned patent it was already pointed out that the grooves which are to be molded into one side of the material should not exceed a depth of to 3.0 percent of the general thickness of the final article or of the part thereof on which a projection is formed because it was found that a deeper compression might result in a deformation of the covering sheet material which would be noticeable on its outer side.
Although this method has proved to be of great advantage, it has been found that, especially near the corners of the molded body, the usual depth of the grooves is often not sufficient in order to produce the required back pressure which is necessary for securely bonding the covering sheet material at all points to the molded body during the hot-molding operation. This, of course, applies especially if the surface of the die is provided with at least a pair of projecting ridges which extend, for example, at right angles to each other, but if for reasons of a more simple manufacture these ridges are not made of such a length that their adjacent ends join each other and form an apex so that the molded body would then be provided with a continuous rectangular groove which extends parallel to two adjacent edges of the body and the apex of which is located adjacent to the rectangular corner between these edges. Thus, since the two adjacent grooves are then separated from each other within an area near the corner of the molded body, this corner area which, as has now been found, should actually be more highly compressed than the other marginal areas will be devoid of any additional pressure and will thus be subject to shrinkage, and the covering layer will therefore be bonded insufficiently to this corner area.
SUMMARY OF THE INVENTlON lt is an object of the present invention to overcome these disadvantages of the method as previously described and to insure that, by impressing recesses from the bottom face, and especially at the corner areas of a molded article which is covered with a thin sheet material, the material within these areas will be so highly compressed during the final hot-molding and bonding of the sheet to the compressed material that a sufficient back pressure will also be exerted at these areas so that the sheet material will be securely bonded thereto. It is another object of the invention to impress recesses of such a shape and in such a manner into the material of the molded body that, due to the shape of these recesses, they may be safely impressed to a considerably greater depth than the elongated groovelike recesses which were impressed by the knownmethod by projecting ridges on one of the dies. By impressing the recesses according to the invention not only in the corner areas from the bottom face of a molded article into the latter, but also in other areas, for example, adjacent to the edges of the article or adjacent to projections on the other side of the article, all of these recesses may be impressed to a greater depth than that to which the v groovelike recesses could be impressed by the known method without danger that the covering sheet material might be deformed or marked on its outer surface. A
For attaining these objects, the present invention provides especially each corner area of the die with a conical or similar projection so as to impress a recess of a corresponding shape from the bottom face of the molded article into the latter at a point which is located 1 on the bisecting line of the angle which is formed by each of the angular or rounded corners of the article.
These conical corner recesses may be provided in combination with groovelike recesses of the type, in accordance with the known method, which preferably extend parallel and adjacent to side faces of the molded body and may either terminate closely adjacent to the conical corner recess which is made of a greater depth than the groovelike recesses or extend into the lower part of the conical corner recess. Since such a conical recess may be safely made of a considerably greater depth than the adjacent groovelike recesses, the comer area of the molded article will be more highly compressed in accordance with the invention than the adjacent marginal parts so that the necessary pressure will also be produced within the angular or rounded corner area to secure the thin sheet material at all points firmly to the upper, lower and lateral faces of the corner area,
for example, ofa plate-shaped element. By making at least each of these corner projections on the die and the corresponding recesses in the molded article of a conical or similar tapering shape, the pressure components will be distributed within the article in such a manner that the covering layer will not be deformed or marked on its outer side even though the depth of the recess from its free outer end to its point-like inner end is made much larger than the depth of one of the groovelike recesses.
The angle of the taper of each conical projection on the die, and especially of each corner projection, is made of such a size that the base diameter of this projection which corresponds to and produces the maximum diameter of the conical recess at the free end thereof is considerably larger than the width of the base of one of the ridgelike projections for molding one of the groovelike recesses. This is true especially when a conical corner recess is employed in combination with two adjacent groovelike recesses which extend parallel to the adjacent edges of the molded article, and it is also true regardless of whether the ends of these groovelike recesses are spaced at short distances from the free outer end of the conical corner recess or whether they terminate in the free outer end of the corner recess.
It-is another feature of the invention to provide the molded article with a row of conical recesses in place of a longer continuous groovelike recess or in place of several shorter groovelike recesses which are separated by ungrooved portions. This has the advantage that due to their shape the conical recesses forming such a row may also be made of a considerably greater depth and a greater width at their outer ends than the groovelike recesses. Such rows of conical recesses may be employed in combination with conical corner recesses by extending substantially parallel to the adjacent edges of the molded article, in which event, however, the conical corner recesses should preferably be made of a greater depth and a greater maximum diameter than those of the adjacent rows. Such a row of rows of recesses may, however, also be impressed into one side of the article to compress the same more highly atanother area or other areas which are provided with a projection or projections on the opposite side of the article. The adjacent conical recesses of such a row may also merge into each other at their larger outer ends, and if employed in combination with larger conical corner recesses, the smaller conical recesses next to such a corner recess may also merge partly into the free end of the larger corner recess.
Although previously and hereafter the recesses according to the invention as well as the die projections for producing these recesses are described as being of a conical shape tapering to a point, they may also be of another tapering shape, for example, of the shape of a pyramid with three or more sides. It is also not absolutely necessary that they taper to a point, but they may also terminate in a small rounded inner end or in a small flat surface.
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a bottom view of a corner part of a plate which is produced in accordance with the invention;
FIG. 2 shows a cross section which is taken along line II-II of FIG. 1, and in which, for better illustration, the covering layer is shown of a thickness considerably greater than its actual thickness;
FIG. 2a shows a partial cross sectional view of a die for forming the plate partially shown in FIGS. 1 and 2;
FIG. 3 shows a bottom view ofa corner part of a plate according to a modification of the invention; while FIG. 4 shows a bottom view of a corner part of a plate according to a further modification of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 of the drawings illustrate one corner part of a plate 3 which is produced in accordance with the present invention. Plate 3 is provided with groovelike recesses 6 which are impressed into the lower side of the plate and each of which extends substantially parallel to and at a certain distance from the adjacent outer edge up to a point near each corner of the plate. Each of these corner parts of plate 3 is provided with a conical recess 7 which is separate from the adjacent grooves 6 and has at its outer end a maximum diameter dwhich is larger than the maximum width b of the outer side of the grooves 6. The body of plate 3, which is molded from a mixture of comminuted fibrous materials, for example, wood chips, and a thermosetting binder in the form of a natural or synthetic resin, is covered on all sides,,with the exception of the deeper inner surfaces of the conical recess 7, and possibly also of the bottom of grooves 6, with a continuous layer 4 and 5 of a suitable sheet material which is bonded together with the body of plate 3 by the hot-molding operation. By the different density of the lines indicating the fibrous mixture of the body of plate 3, FIG. 2 illustrates the higher rate of compression V which is attained within the corner area of plate 3 by impressing the conical recess 7 into its lower side to a depth T which is considerably deeper than the depth 1 of the adjacent grooves 6.
The plate 3 described above and illustrated in part in FIGS. 1 and 2, in press-molded in a two-part mold or die D and D; as illustrated in FIG. 2a which, when closed, as shown in FIG. 2a, defines a mold cavity C. The lower-mold part D is provided with ridges 6' projecting upwardly from the upper surface of the lowermold part, and are inwardly spaced from and substantially parallel to the side faces thereof which define the mold cavity C. These ridges 6 end short of the corner portions of the cavity, and a substantially conical projection 7 is provided in the region of each corner portion of the cavity and likewise projects upwardly from the upper surface of the mold part D A preformed blank of a mixture of comminuted fibrous material and a thermosetting binder, covered on all sides except for the abovenoted exceptions with a continuous layer of a suitable sheet material, is placed between the two parts of the mold and the latter is then closed under application of heat and pressure thereto to harden the thermosetting binder and at the same time to bond the sheet material together with the body of the plate 3. During closing of the mold, the ridges 6 and the conical projections 7 will penetrate into the bottom face of the blank to provide the latter with groovelike recesses 6 and conical recesses 7 as described above. Thereby, the comminuted fibrous material is more highly compressed in the region of the ridges 6, and especially in the region of the conical projections 7', which have, as shown in FIG. 2a, a height greater than that of the ridges. This greater compression of the blank in the region of the ridges and the conical projections will prevent shrinking of the plate during setting of the molding mixture in the final hot molding operation, especially since the aforementioned ridges and projections will penetrate during such molding operation into the recesses formed thereby. This in turn, will assure proper bonding of the outer sheet to the body of the plate 3 during the hot molding operation since any relative shifting of the adjacent surfaces of the outer sheet and the body of the plate during the final hot molding operation is thus prevented.
FIG. 3 shows a bottom view of a corner part ofa plate 3 which is provided with groovelike recesses 6 and deeper conical corner recesses 7 according to a modification of the invention. The ends of grooves 6, which again extend substantially parallel to the outer edges of plate 3, merge into the wider lower parts of the corner recesses 7. Or course, it is also possible to extend only one of the grooves 6 into the lower part of the conical corner recesses 7, while the other groove 6 terminates at a short distance from this corner recess 7.
The mold for producing the plate shown in part in FIG. 3 is similar to the mold described above in connection with FIG. 20, but differs therefrom in that, in this case, the ridges in the bottom part of the two-part mold extend up to and are joined to the conical projection provided at each comer.
FIG. 4 shows a bottom view of a corner part of another plate 3 into the lower side of which two rows of conical recesses 8, which extend substantially parallel to the adjacent edges of plate 3, are impressed in place of the grooves 6 as shown in FIGS. 1 and 2. Since, according to the invention and for the reasons as previously stated, the conical corner recesses 7 are preferably made deeper than the recesses 8 adjacent to the lateral edges of plate 3, the diameters of the outer ends of the corner recesses 7 are preferably also made larger than those of the recesses 8 of the lateral rows. However, if desired, the diameters of the outer ends and/or the depths of all of the conical recesses 7 and 8 may also be made of the same size or sizes.
The mold for producing the plate partly shown in FIG. 4 is similar to the mold described above in connection with FIG. 2a but, instead of longitudinal ridges 6, there are provided rows of substantially conical projections for forming the recesses 8 which have, however, a smaller maximum diameter and a shorter height than the corner projections for forming the recesses 7 at each comer of the plate.
As has also been previously mentioned, the recesses 7 or 8 may also be made of a tapering shape other than conical, for example, of a pyramidal shape with three or more sides. In such an event, it may be of advantage to make the different sides of each pyramid of different inclinations relative to the plane surfaces of the upper and lower sides of plate 3, for example, by making the sides of the pyramids facing the outer edges and corners of the plate of a steeper inclination than the inwardly facing sides. Of course, if the recesses 7 or 8 are made of a conical shape, their axes may be similarly inclined toward the corners or toward the lateral edges of plate 3.
Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments but is capable of numerous modifications within the scope of the appended claims.
Having thus fully disclosed my invention, what I claim is:
l. A method of making from a mixture of comminuted fibrous material and a thermosetting binder a substantially plate-like polygonal element having a top face, a bottom face and a plurality of side faces extending at angles relative to each other and defining a plurality of edges and corners of said element, comprising:
a. press-molding from said mixture said element under application of heat and pressure thereto with a thin cover sheet applied to respective faces thereof;
b. compressing said element while activating said thermosetting binder and simultaneously impressing into said element along edges of said bottom face thereof recess means having a predetermined depth and extending parallel to the respective edges, and in the region of each corner thereof a corner recess opening in said bottom face and taper-ing in direction towards said top face substantially to a point and having a depth greater than said predetermined depths of said recess means; and
C. maintaining the thus compressed and impressed element in compressed condition at least until said activated thermosetting binder has set so as to bond said fibrous material and said cover sheet thereto and to prevent shrinkage of said element in said corner regions thereof during said setting of said thermosetting binder.
.2. A method as defined in claim 1 wherein each of said corner recesses has a conical shape.
3. A method as defined in claim 1 wherein each of said corner recesses has a pyramidal shape having at least three sides.
4. A method as defined in claim 1 wherein each of said corner recesses is impressed into said element so as to have at said bottom face adimension'greater than the width of said recess means at said bottom face.
5. A method as defined in claim 1 wherein said recess means are impressed in the form of elongated grooves.
6. A method as defined in claim wherein said grooves are impressed in such a manner that they end short of said corner recesses 7. A method as defined in claim 5 wherein said 8. A method as defined in claim 1 wherein said recess means are in the form of a row of consecutive recesses.
9. A method as defined in claim 8 wherein each of grooves are impressed in such a manner that they inter- 5 sad conseiutwe recesses has a conical p sect said corner recesses.