HK1028888B - Method of manufacturing a molded door skin from a wood composite - Google Patents

Description

Method for producing a molded door facing from a wood composite material

Technical Field

The disclosed invention relates to a method for manufacturing a molded door facing from a wood composite material, to the door facing (or trim panel) so produced, and to a door made from such door facing. More particularly, the disclosed invention relates to a method of manufacturing a molded door facing wherein a solid wood composite blank is heated in a press to a temperature sufficient to soften the blank, then the press platens are pressure actuated to bring them into close proximity with each other and thereafter the pressure is periodically increased, thereby deforming the blank into a molded configuration suitable for a door facing, and finally assembling the door facing into a door.

Background

Hollow doors are used both as inner and outer doors. The hollow core door may be a flat door, i.e. both major faces are flat or planar. Hollow core doors may also be "molded" doors, i.e., having a plurality of three-dimensional panels that form a door facing when manufactured. The molded door facings are relatively expensive because of the high capital costs associated with the need for molds, presses, etc. Flat doors, on the other hand, are relatively inexpensive but do not have the aesthetic features that are sometimes desired by consumers.

Many hollow core doors are made from door facings formed from wood composite materials. These wood composite materials include particle board, particle board and medium density fiberboard ("MDF"). Wood-based composites employ a resin binder, typically a thermosetting resin, to maintain the solid shape of the wood fibers that make up the composite. Such wood composite materials are not moisture impermeable and therefore doors employing such facings are not suitable for exterior doors. If this composite material absorbs moisture, either liquid or gas, the door components swell and deform the door. Fiberglass and steel doors do not have this problem of water absorption and, therefore, are more used for exterior doors.

Due to the cost difference between flat door facings of wood composite materials and molded door facings of wood composite materials, attempts have been made to convert flat door facings to molded door facings. Those prior art efforts have not resulted in a commercially acceptable door facing, primarily due to the unsatisfactory appearance of the surface. Prior efforts to convert flat door facings to molded door facings have generally resulted in cracking, marring or other aesthetically undesirable structures and appearances.

Standard molded door facings are formed from thicker mats or blocks of material that are subsequently extruded in a press to a thinner thickness. The moisture content of such a block is large and water is pressed out during the pressing operation. Because the block is in a fluid-like state during extrusion, the resulting veneer has consumer-acceptable angular characteristics because the wood fibers can flow to follow the shape of the die. Due in part to the high investment in manufacturing molded door facings, manufacturers often desire a single order to order a large number of door facings in order to maximize production efficiency. Small orders make the price prohibitive.

Those skilled in the art will recognize that there is a need for a method of making molded door facings from wood composite materials that can produce molded door facings having consumer acceptable characteristics and surface features using a standard flat door facing blank as the base material. Another need in the art is a door made from wood composite door facings that has a suitable resistance to moisture so that the door can be used as an exterior door. The disclosed invention satisfies these and other needs in the art.

Disclosure of Invention

A primary object of the invention disclosed herein is a method for making door facings from wood composite blanks by periodically applying an increasing pressure to a softened blank to produce a facing having consumer acceptable characteristics and surface features.

Another object of the invention is a door facing that is impermeable to moisture so that the door does not deform and is therefore suitable for use as an exterior door.

A method of manufacturing door facings in accordance with the present invention includes the step of providing a flat blank of wood composite material. The blank is placed between the platens of a heated press, which is heated to a temperature sufficient to soften the resin in the blank, thereby softening the blank. Sufficient pressure is applied to close the platens and then (possibly periodically) incrementally applied pressure is applied to deform the blank to a stamped shape determined by the shape of the platens and degas the blank. The blank is then removed from between the platens.

The door facing according to the present invention comprises a three-dimensional blank of molded medium density fiberboard. The blank has a first portion of a first predetermined thickness. The blank has a second portion of a second predetermined thickness. The second thickness is less than the first thickness.

A door facing in accordance with the present invention comprises a three-dimensional blank of molded medium density fiberboard having a density of about 800 to about 1000Kg/m³。

A door in accordance with the present invention includes a perimeter frame having oppositely disposed sides. First and second molded door facings are provided. Each door facing has first and second sides. Each first side of each door facing has a moisture impermeable barrier layer integrally applied thereto. The second side of each door facing is secured to one side of the frame.

These and other objects and advantages of the present invention will be apparent in the following description and the accompanying drawings.

Drawings

The above and other objects, advantages and novel features of the invention will become apparent from the following detailed description of preferred embodiments of the invention when considered in conjunction with the drawings, in which:

FIG. 1 is a simplified flow diagram of a process for making the door facing of the present invention;

FIG. 2 is a partial cross-sectional view of a flat blank for use in the present invention;

FIG. 3 is a partial cross-sectional view of the molded door facing of the present invention;

FIG. 4 is a partial cross-sectional view of the blank shown in FIG. 2 between platens of a press for the present invention;

FIG. 5 is a graph illustrating pressure over time in a first cycle in accordance with an embodiment of the present invention;

FIG. 6 is a graph showing pressure over time in a second cycle in accordance with the present invention;

FIG. 7 is a side view of a molded door according to the present invention; and

fig. 8 is a partial cross-sectional view taken along line 8-8 in fig. 7.

Detailed Description

A flat wood composite blank 10 is best shown in fig. 2 and has oppositely disposed parallel flat surfaces 12 and 14. The blank 10 is preferably a wood composite material, such as a medium density fiberboard, bonded together by a thermosetting resin. MDF (medium density fiberboard) typically uses urea formaldehyde resin as a binder, which softens or melts at between 320 ° F (160 ℃) and about 425 ° F (218 ℃). MDF of different thickness and weight can be used, ranging between 4mm and 7 mm. I prefer a relatively thick blank 10 to obtain a lignocellulosic material that can be stretched during extrusion to provide a crisp, well-defined character.

By the process shown in fig. 1, the flat blank 10 is converted into a die overlay 16 best shown in fig. 3. Fig. 3 shows a design 18 formed in a facing for providing aesthetics, such as a facing for a door 20 shown in fig. 7. The overlay 16 of fig. 3 has opposed surfaces 22 and 24 formed from the surfaces 12 and 14 of the blank 10. The overlay 16 has parallel first and second portions 26, 28, each having a different thickness due to the different stretching process used to form the overlay 16. If the thickness of the blank 10 is 4mm, the thickness of the first portion 26 of the portion of the major surface forming the facing is slightly less than 4mm and the thickness of the second portion 28 is approximately 3mm due to the extrusion resulting from the drawing of the blank 10 to form the design 18. The second portion 28 is formed integrally with the planar first portion 26 by angled portions 30 and 32. The angled portions 30 and 32 preferably have a configuration that allows the facing 16 to be easily removed from the platens of the press at the conclusion of the forming process.

The flat blank 10 is received at a loading station 32 in fig. 1. The density of the blank 10 is about 750 to about 800Kg/m³And has a thickness of about 4mm to about 7 mm. The initial moisture content of the blank 10 was 8% by weight.

The blank 10 is then advanced to a sealing station 36 where a sealant is applied by roll coating, spray coating or curtain coating. The weight of the applied sealant is from about 2 to about 3gm/ft²The sealant is applied only where the outer surface of the facing 16 will be formed from the blank 10, while the opposite side 22 may be exposed to the wood fibers to receive white glue (PVA) for adhering the facing 16 to the portal. The sealant may be dried at 38, such as with an infrared lamp.

The sealant applied to the surface 14 may contain a pigment agent, for example, when the door 20 is an interior door suitable for painting. Many sealants are known in the art. The sealant is preferably an impression sealant such as that available from Akzo Noble. The sealant aids in cleaning the mold, increases the elasticity of the wood fibers, and improves the formation of surface features.

The billet 10 is then preferably and optionally transferred from the dryer 38 to a steam kettle 40. The billet 10 is exposed to low pressure saturated steam within the kettle 40. In the kettle 40, the temperature of the billet 10 increases and the billet 10 also absorbs water, so that it exits the kettle 40 with a water content of about 15 to about 20% by weight. As previously mentioned, the resin bonding the wood composite material and the wood fibers in the blank 10 is a thermosetting resin, and as the temperature in the kettle 10 increases, a remelting process of the resin is initiated, thereby making the blank 10 softer.

I have also found that the increase in water content in kettle 10 can be facilitated by sanding the sealant-free surface 12 of blank 10. Sanding surface 12 may remove resin from the surface, thereby increasing moisture absorption. It is known to those skilled in the art that the wood fibers swell after absorbing water, and therefore the purpose of applying steam in kettle 40 is to expand the wood fibers so that they may be stretched during subsequent forming processes, as well as to melt the resin to soften blank 10.

I have found that low pressure steam should be used in kettle 40. And note how long the billet 10 is exposed to the kettle 40. If the blank 10 is exposed to steam for less than 30 seconds, the absorbed moisture may be insufficient to swell the wood fibers and not heat enough to soften the resin. If the blank 10 is exposed to steam for too long, for example more than one minute, i find that the surfaces 12 and 14 of the blank 10 are susceptible to blistering and discoloration. If the surface is blistered or discolored, the finished veneer may not be suitable for use as a commercially acceptable door veneer, or may require further processing.

While I claim exposing the blank 10 to moisture in the form of steam, one skilled in the art will recognize that other methods may be used. For example, a water mist may be sprayed onto the surface of the blank 10 and then subjected to microwave or infrared heating. Regardless of the application, it is desirable to absorb moisture in order to facilitate swelling of the wood fibers. As explained elsewhere, in some cases where a longer squeeze time can be achieved, absorption of moisture is not necessary. If a steam kettle 40 is used, the cycle time can be as fast as 90 seconds for a 4mm thick MDF billet 10.

After exiting the steam still 40, the blank 10 may be conveyed to a barrier station 42 where a moisture impermeable barrier is applied to the sealant on the outer surface 14. The moisture impermeable barrier layer need only be applied to the door facing intended for use as an exterior door. I claim that the moisture impermeable barrier layer is a melamine impregnated phenolic crepe paper applied to the sealant. Applicable paper can use SWEDOTEC^The flexible carrier films TGPN and TXP, which are available from Akzo Nobel under the trade name, claim the use of a crepe paper substrate for applying the resin because the coefficient of expansion of the crepe paper is sufficient to accommodate the swelling that occurs when the design 18 is formed. Thus, the crepe paper does not peel, tear, or otherwise present a discontinuous surface into which moisture can penetrate. It will be appreciated by those skilled in the art that the crosslinked polymeric resin system forming the water repellent layer may also be sprayed or otherwise applied to the surface 14 as a two-component liquid. Other water resistant layers may also be used.

Another advantage of the crepe paper barrier layer is that it can be colored so that a wood particle or other pattern or decoration can be applied to the formed surface 24. The moisture impermeable barrier also increases the hardness of the door facing and provides a wear resistance. The improvement in wear resistance is helpful during shipping because both the facings and doors are easily scratched or otherwise damaged during shipping. The resin takes 40 seconds to cure and seal the veneered surface. The portion of the blank 10 that is stretched to form the design 18 is prone to swelling, and the water resistant layer reduces this possibility.

The blank 10 is then transferred to a press 44 where the profile shown in figure 3 is pressed. I claim to use a high pressure press of about 2000 tons to apply a pressure of up to 1.5 tons per square inch (i.e., 6.45 square centimeters) to the billet 10 during the pressing operation. The press 44 has platens 46 and 48, as best seen in FIG. 4. The platens 46 and 48 are preferably each of chrome plated steel dies, and a hard chrome plating preferably has a hardness of 70 rockwell. I claim that the surfaces 50 and 52 of the platens 46 and 48 have a hard chrome plating to prevent xylose buildup that might otherwise occur.

The thickness of each platen 46 and 48 is preferably about 4 inches (i.e., 10.16 cm). Each platen 46 and 48 is heated. I claim that platens 46 and 48 be electrically heated, such as with Carl bars (Kalrod), although oil or steam circulation is also an acceptable thermal medium. But i claim to maintain the platens at a higher temperature of between about 320F (160 c) to about 425F (218 c), more preferably between 370F (187 c) to 380F (193 c) when heated. This elevated temperature should be maintained throughout the extrusion operation for about 90 seconds to ensure that the bonding resin in the billet 10 re-melts and remains flowable during extrusion.

The platen 46 has a male mold member 54 and the platen 48 has a female mold member 56. Preferably, the modules 54 and 56 are mirror images to prevent the formation of variations in the thickness of the finished door facings. The press 44 causes the portion of the blank 10 forming the design 18 to expand or stretch, and thus, if the die pieces 54 and 56 are not mirror images, thickness variations occur that result in uneven flow of the softened wood composite material. Although only a single module 54 and 56 is disclosed in FIG. 4, it will be understood by those skilled in the art that the molded door shown in FIG. 7 has several mating pieces of such modules, the specific number and shape depending on the structure, size and appearance of the door.

I have found that by initially softening the billet 10 in the steam kettle 40 and then extruding the billet 10 between the platens 46 and 48 in a periodically pressurized manner, the billet 10 can be converted into a commercially acceptable molded door facing 16. Further, I have found that an acceptable molded door facing 16 can be formed if the press 40 has means for allowing the blank 10 to de-air in order to evacuate air, steam and other volatile substances that would otherwise form bubbles in the surface of the door facing. The degassing can be obtained by opening both platens, which is shown in the graph of fig. 5, or by providing an outlet on the platen, which is shown in the graph of fig. 6. Regardless of how degassing is achieved, I have discovered that an acceptable molded door facing can be formed by periodically applying pressure at any increased level to induce flow of the wood fibers and resin until the desired profile is achieved, while providing a means for venting gases.

Fig. 5 discloses the variation of pressure in the press 40 over time with the platens 46 and 48 periodically opening to release gas from the blank 10. As best shown in fig. 5, the blank 10 is placed between the platens 46 and 48, such as shown in fig. 4, within the confines of reference numeral 58. The pressure is then increased to a first predetermined pressure more slowly in the range of 60. Once the first predetermined pressure is reached, the pressure is maintained for a period of time sufficient to further heat the resin and initiate flow of the wood fibers and resin, a process which is generally indicated at 62 in fig. 5. The platens 46 and 48 are then opened at 64 and the billet 10 is degassed at 66. The pressure is then increased at 68 and maintained at 70. The pressure maintained at 70 is greater than the pressure maintained at 62. The rate of increase in pressure at 68 is much faster than the slower increase at 60 because I have found that the slower rate of pressure increase initially places less stress on the wood fibers and resin. Because they are stiffer and in an expanded state, they move more slowly. After the preliminary structure of the veneer 16 is achieved by the pressure applied at 62, the next cycle aims to make the outline of the shaped design element 18 more prominent, while also smoothing the surface 24 by allowing resin to accumulate on the surface.

After maintaining the pressure at 70, the platens 46 and 48 are again opened at 72 to enable degassing at 74. The pressure is increased at 76 and maintained at a higher level at 72 than at 70 and then released at 80 to enable degassing at 82. Pressure is then rapidly applied at 84, held at 86, and released at 88. Degassing occurs at 90, followed by application of pressure at 92, maintaining pressure at 94, and releasing pressure at 96. The door facings 16 may then be removed at 98.

I have found that pressures 70, 78, 86, and 94 should be higher than the peak pressure of the cycle immediately preceding them. The peak pressure at 94 may be 1.5 tons per square inch (i.e., 6.45 square centimeters), which is a relatively high pressure. I have also found that the end holding periods 86 and 94 should be longer than the previous periods 62, 70 and 78 to provide better styling of the design 18. I claim that the peak pressure between 3 and 6 pressure cycles is increasing. This increasing peak pressure, in combination with maintaining the platens 46 and 48 at an elevated temperature, causes the wood fibers to change their state to form the contours of the design 18, maintains a higher softening of the blank 10, and improves the surface finish of the surface 24, making it commercially acceptable and suitable for painting, painting and other decoration.

I have found that the number of press cycles and the proximity of the platens 46 and 48 varies depending on the thickness of the blank 10 and the material from which the blank 10 is constructed. The pressure may be controlled by either adjusting the space between the platens 46 and 48 or adjusting the pressure applied to the platens 46 and 48 to bring them into proximity. Typically, only one of the platens 46 and 48 is movable relative to the other, so that controlling the hydraulic pressure applied to the movable platen effectively controls the pressure cycling.

As noted above, while i claim that the billet 10 is immersed in water in the steam kettle 40 in order to soften the resin and swell the wood fibers, this is not necessary if the pressing cycle is long enough. In this case, the blank 10 is dry when placed in the press 44, with a moisture content of about 8%. As the platens 46 and 48 are heated, they provide sufficient heat by radiation to soften the resin and thus the blank 10. While the wood fibers in the billet 10 do not swell and therefore have additional enhanced flow, longer extrusion cycles minimize the effect in this regard.

Figure 6 discloses a pressure time-varying cycle in which platens 46 and 48 are provided with outlets to allow degassing. This eliminates the need to open the platen, but I have found that it is still necessary to continually increase the peak pressure and maintain it.

The blank 10 is placed into a mold at 100 and the pressure is slowly increased at 102. The pressure is maintained at 104 and then increased again at 106. It should be understood that with the use of platens 46 and 48 with the outlets, degassing occurs substantially continuously throughout the extrusion cycle. The pressure is maintained at 108 and then increased at 110. The pressure is increased at 114 and maintained at 116. The pressure is increased at 118 and maintained at 120. The pressure is increased at 122, maintained at 124, and then decreased at 126 to remove the blank 16 at 128.

I have found that the moisture content of the door facings 16 removed after completion of the extrusion cycle shown in fig. 5 and 6 is from about 3% to about 4% by weight. Thus, the moisture content of the blank 10 is significantly reduced during the forming process due to the heat applied by the platens 46 and 48. In addition, the density of the finished door facing 16 is about 800 to about 1000Kg/m³Higher than the density of the blank 10. The increased density makes the door facing 16 stiffer, which improves the strength of the formed door. Furthermore, the increased density provides a better surface for painting. The increased density facilitates extrusion by the platens 46 and 48 acting on the billet 10.

The formation of the design element 18 expands or stretches the portion of the blank 10 forming the design element 18 by about 15% to about 25% of its length, as shown by arrow a-a in fig. 3. Further, the portion 28 of the design 18 has a reduced thickness on the order of about 25% because of the increased strength required to provide the wood fibers.

After the door facing 16 is removed from the press at 98 or 128, it is transported to a reforming station 130 where the door facing 16 is trimmed, cleaned and re-humidified to a moisture content of about 8%. If a creped paper barrier is used, no clean handling is necessary. Re-humidification may be obtained by water mist or the like. After rearrangement, the door facings are conveyed to a door forming station 132 where the door facings are adhered to a portal, preferably a wood portal, to form a door. Fig. 7 discloses an example of a door. If the door 20 shown in fig. 7 is an exterior door, another moisture impermeable barrier may be applied to the exposed edge of the door frame by edge bonding.

Fig. 8 discloses a partial cross-sectional view of an outer door in accordance with the present invention having a molded door facing 16 bonded to a door frame 136, such as with PVA. As known to those skilled in the art, the door frame 136 extends around the perimeter of the rectangular door facing 16 and generally includes two wooden stiles extending along longitudinal edges and two horizontal and vertical rails. Further, although I disclose that the door facings 16 are spaced apart, they may have a core, such as foam, therebetween.

Melamine impregnated phenolic crepe paper 138 is laid generally around the outer surface 24 of the outermost door facing 16. As described above, melamine impregnated phenolic crepe paper 138 provides a moisture impermeable barrier that minimizes moisture absorption by door 20. Other cross-linkable, water-resistant layers may of course be used in the present invention. To increase the water blocking effect of the door 20 shown in fig. 7, an additional moisture impermeable barrier 140 may be applied to the exposed edge 142 of the door shelf 136 and the edge 144 of the door facing 16. The further water barrier 140 may also be a melamine impregnated phenolic resin crepe paper. I have found that the crepe paper is so thin that it can cover the layer 138 without creating an undesirable appearance on the surface. The water resistant layer 140 must also be cross-linked, which can be achieved by infrared heating or the like. The water-resistant layers 138 and 140, as well as the surface 24 without a water-resistant layer, are suitable for painting, coloring, and other decoration.

While this invention has been described as having a preferred design, it is to be understood that the general principles of the invention may be further modified, utilized and/or adapted in accordance with the teachings of the present invention and that such modifications may depart from the disclosure, insofar as they are within the scope of the common general practices known in the art to which this invention pertains and which are applicable to the essential features of the invention set forth herein and within the scope of the invention as defined by the appended claims.

Claims (30)

1. A method of manufacturing a door facing comprising the steps of:

a) providing a wood composite flat blank;

b) placing the blank between heated platens of a press, heating the platens to a temperature sufficient to soften the resin in the blank, thereby softening the blank;

c) applying sufficient pressure to close the platens and then applying pressure in incremental pressure levels to deform the blank to a molded shape determined by the shape of the platens and degas the blank; and

d) the molded blank is removed from between the platens.

2. The method of claim 1, comprising the steps of:

a) the pressure is applied to the platen periodically for at least three cycles in an increasing degree of pressure.

3. The method of claim 2, comprising the steps of:

a) no more than six cycles of pressure are applied to the platen.

4. The method of claim 2, comprising the steps of:

a) the pressure is applied to a first predetermined level during a first period, the pressure being applied for a longer period than the time it takes to apply the pressure during any subsequent period.

5. The method of claim 2, comprising the steps of:

a) the pressure is maintained in the last cycle for a period of time that exceeds the time the pressure is maintained in the first cycle.

6. The method of claim 4, comprising the steps of:

a) the pressure is maintained in the last cycle for a period of time that exceeds the time the pressure is maintained in the first cycle.

7. The method of claim 6, comprising the steps of:

a pressure of 1.5 tons per 6.45 square centimeters is applied.

8. The method of claim 2, wherein the pressure is applied periodically at a pressurized level, the method comprising the steps of:

a) the pressure is reduced at the end of each cycle.

9. The method of claim 8, comprising the steps of:

a) the pressure is reduced to a predetermined basic level at the end of each cycle.

10. The method of claim 2, wherein the pressure is applied periodically at a pressurized level, the method comprising the steps of:

a) during each cycle, a predetermined level of pressure is maintained for a predetermined time.

11. The method of claim 10, comprising the steps of:

a) the pressure is maintained at a predetermined level in each cycle that exceeds the level at which the pressure was maintained in the immediately preceding cycle.

12. The method of claim 10, comprising the steps of:

a) the pressure is increased to the pressure of the immediately next cycle as soon as a predetermined time has elapsed.

13. The method of claim 12, comprising the steps of:

a) the pressure is maintained in the last cycle for a period of time that exceeds the time the pressure is maintained in the first cycle.

14. The method of claim 13, comprising the steps of:

a) the pressure is reduced to a basic level as soon as time passes in the last cycle.

15. The method of claim 1, comprising the steps of:

a) the moisture content of the flat blank is increased to a preselected amount prior to placing the blank between the platens.

16. The method of claim 1, comprising the steps of:

a) the flat billet is exposed to low pressure steam in order to increase its moisture content.

17. The method of claim 15, comprising the steps of:

a) the flat billet is exposed to saturated steam for a period of time to increase the moisture content to 15% to 20% by weight.

18. The method of claim 1, comprising the steps of:

a) the platens were maintained at a temperature of 160 ℃ to 218 ℃.

19. The method of claim 18, comprising the steps of:

a) the platens were maintained at a temperature of 187 ℃ to 193 ℃.

20. The method of claim 15, comprising the steps of:

a) the platens were maintained at a temperature of 160 ℃ to 218 ℃.

21. The method of claim 1, comprising the steps of:

a sealant is applied to a first major planar surface of the flat blank prior to increasing the moisture content.

22. The method of claim 21, comprising the steps of:

a) a colored sealant is applied.

23. The method of claim 20, comprising the steps of:

a) the sealant is allowed to dry before increasing the moisture content.

24. The method of claim 1, comprising the steps of:

a) a water resistant layer is applied to a major planar surface of the blank prior to placing the blank between the platens.

25. The method of claim 24, comprising the steps of:

a) a cross-linked water-resistant layer is applied to the major planar surface of the flat blank prior to placing the blank between the platens.

26. The method of claim 1, comprising the steps of:

a) a melamine impregnated or phenolic resin water barrier is applied to the major planar surface of the flat blank before the blank is placed between the platens.

27. The method of claim 25, comprising the steps of:

a) a melamine or phenolic resin is provided as a water barrier.

28. The method of claim 1, wherein degassing is performed by releasing pressure between at least two pressure application cycles.

29. The method of claim 1, wherein degassing is performed via at least one vent in at least one platen.

30. The method of any one of claims 1 to 29, wherein the billet is periodically pressurized and degassed with increasing pressure levels.