FIELD OF THE INVENTION

The present invention is related to manufacturing of health safe structural anti-bacterial plywood. More particularly the present invention relates to an innovative treatment of plywood made to ensure a defect free product along with additional features like fire retardant properties, acoustic properties & most importantly anti-bacterial properties.
The whole process involves manufacturing of the plywood through MAT process for the core ply and then overlaying it with 4 face veneers to give additional strength.

BACKGROUND & PRIOR ART
Plywood is a composite wood product which is manufactured by joining layers of sliced veneers with adhesive under specified temperature & pressure. The temperature & pressure is applied on the glued sliced veneers is done on a Hot Press which is a mechanical device.
The above conventional process of Plywood manufacturing requires high pressure & temperature which ensures that the plywood made is flat but cannot guarantee an even thickness, zero gap in core, perfect bonding and uniform surface as the process is very old made with conventional machines.
To eliminate the above defects and to ensure a strong structural grade plywood, the invention has been done.
The present invention describes a state of the art technology of the anti-bacterial, fire retardant structural plywood. The manufacturing process adds strength to the plywood with zero defect and gives the additional benefits to the end customer like calibrated thickness, fire retardant, acoustically effective & being health safe with anti-bacterial coating.
In the prior art a Chinese specification CN107139281A discloses antibacterial and anti-mite plywood structure and manufacturing method thereof. The antibacterial and anti-mite plywood structure comprises a plywood body, a wearing plate, anti-mite plates, a moisture absorbing plate and a fireproof plate, wherein the anti-mite plates are glued at the top and the bottom of the plywood body, and the moisture absorbing plate is glued on the anti-mite plate close to the bottom of the plywood body; the fire-proof plate is glued on the anti-mite plate close to the top of the plywood body; and the wearing plate is glued on the side, far away from the anti-mite plate, of the fire-proof plate. According to the antibacterial and anti-mite plywood structure and the manufacturing method thereof, the plywood body is soaked in an anti-mite finishing agent, and an anti-mite finishing agent solution is added into glue, so that the plywood body is subjected to double-layer protection, accordingly, the anti-mite and antibacterial performance of the plywood body is effectively improved, and a safety guarantee is provided for the indoor life of users; and meanwhile, the anti-mite finishing agent is a DM-3031D anti-mosquito finishing agent, so that the mosquito repelling and disinfecting effects are achieved.
In another prior art a Chinese utility model CN202716505U discloses a wear-resisting anti-bacterial water-fast bamboo plywood. The wear-resisting anti-bacterial water-fast bamboo plywood which comprises a bamboo plywood body (1), and a layer of folium cortex eucommiae aqueous extract coating (2) is coated on the whole bamboo plywood body (1) and wrapped with a layer of ultraviolet (UV) painting coating (3). The wear-resisting anti-bacterial water-fast bamboo plywood has the advantages of being low in construction cost, noble in appearance material quality, wear-resisting, anti-bacterial and water-fast.
In another prior art a Chinese application CN107261796A discloses anti-bacterial formaldehyde removal purifying agent and preparation method thereof. The anti-bacterial formaldehyde removal purifying agent comprises water and the following components: 0.1 to 10 wt percent of chitosan oligosaccharide, 5 to 200 ppm of complex silver ions, 0.1 to 10 wt percent of osmotic active ingredients, and 0.1 to 5 wt percent of a film-forming agent. The method comprises the following steps: adding the chitosan oligosaccharide into deionized water, and stirring to enable the chitosan oligosaccharide to be dissolved, so as to obtain a chitosan oligosaccharide solution; sequentially adding the osmotic active ingredients, a complex silver ion solution and the film-forming agent into the chitosan oligosaccharide solution, uniformly stirring to enable the components to be completely dissolved, adjusting the pH of the solution, adding water to constant volume, and then performing suction filtration through a micro-filtration membrane, so as to obtain the anti-bacterial formaldehyde removal purifying agent.
In yet another prior art, a Japanese application JPH08209064A disclose antimicrobial coating material for fancy plywood. The antimicrobial coating for a fancy plywood comprises (A) an antimicrobial and antifungal component consisting essentially of at least one antimicrobial and antifungal substance comprising at least one and/or plural antimicrobial ionic sources selected from the group consisting of silver, zinc and metallic compounds thereof and a zirconium phosphate ceramic material adsorbing and supporting antimicrobial ions thereon, (B) PE wax fine particles having =3µm average particle diameter, (C) a two-part type acrylic-modified urethane-based coating and (D) a thinner. The amount of the contained component (A) is preferably 0.1-3 pts.wt. based on 100 pts.wt. total amount of the components (B) and (C) and the component (B) is preferably used at (0.05/1) to (1/1) ratio of the components (A)/(B).
In yet another prior art, a Chinese application CN103978773A discloses antibacterial terpolycyantoamino-formaldehyde resin impregnated veneer. The said antibacterial terpolycyantoamino-formaldehyde resin impregnated veneer which is characterized in that the veneer is prepared by steps as follows: synthesis of terpolycyantoamino-formaldehyde resin, preparation of a terpolycyantoamino-formaldehyde resin veneer impregnation adhesive, preparation of a antibacterial terpolycyantoamino-formaldehyde resin veneer impregnation adhesive, manufacturing of antibacterial impregnated veneer and the like. The prepared veneer can be directly adhered, under a certain technological condition, to the surface of an artificial board, timber and the like which have antibacterial requirements. After adhesion, the surface of a product needs no finishing treatment, and the surface has good antibacterial performance, heat resistant, wear resistance and the like.
In yet another prior art, a Chinese application CN101733983A discloses an inorganic nano-silver mildew-proof antibacterial healthy decorative veneer and manufacturing method thereof. The method comprises the following steps: (1) soaking a decorative veneer in aqueous solution of nano-silver, and drying the decorative veneer; (2) coating adhesive containing inorganic nano-silver on the surface of a base material; and (3) applying the decorative veneer on the adhesive on the surface of the base material, and performing compression molding on the veneer.

OBJECTIVE OF THE INVENTION
The main objective of the invention is to offer to the customer plywood which is superior in quality than conventional plywood loaded with additional benefits. The plywood made through this process would have zero defects as well as would be calibrated for thickness and shall have anti-bacterial coating. The plywood would additionally have fire retardant properties and shall be acoustically effective.
Yet another object of the present invention is to make durable plywood which will not delaminate at high temperature or long exposure to outdoor condition.
Yet another object of the present invention is to make plywood with clean surface so that it can be painted to give" agreeable surface look.
Yet another objective of the present invention is to develop a combination of anti-bacterial and fire barrier coating which is relatively inexpensive, simple to apply, and which requires modification of the procedures or equipment presently used in the manufacture of plywood.
Yet another objective of the present invention is to develop a fire barrier coating which in itself has sufficient adhesion to the various laminates / veneer used in plywood construction to substitute for the currently used bonding glues, and/or be compatible with those glues, so that they may be applied together utilizing existing equipment.
Still other objectives will become evident as the teachings of this invention are disclosed.
SUMMARY OF INVENTION
One aspect of the invention is a• process of manufacture of fire retardant and anti-bacterial plywood comprising the steps of : Selection of timber; Peeling of veneer from timber; Tenderizing the peeled veneers; Drying the tenderized veneers to achieve upto 8% moisture in the veneers; Conditioning of the dried veneers for 24 hrs; Presetting of veneers through core composing and through panel making; Assembling with phenol formalin glue; Cold pressing (pre-pressing) the assembled veneers to form the base ply shape; Hot pressing the already cold pressed material to make the base ply or MAT ply; Calibration of the base/MAT ply to give it a uniform thickness and a smooth top surface for applying face veneer; Overlaying with face veneer to put a face veneer on top and bottom; Cold pressing the overlaid base ply; Overlying second time with 2 more face to give additional strength; Again, cold pressing the overlaid ply second time; Hot pressing the cold pressed ply; Trimming the edges of the ply to give it a final cut as per market requirement; Sanding the ply to give it a smooth surface; Dipping the ply in preservative solution for anti-borer and anti-termite property addition; Giving it a coating of anti-bacteria solution to kill bacteria in the ply; and Marking and stamping the final graded product.

DETAILED DESCRIPTION OF THE INVENTION
In the below paragraph a detailed and non-limiting description of the main features & process of the invention is given.
All through the specification including the claims, the technical terms and the abbreviations are to be interpreted in the broadest sense of the respective terms, and include all similar items in the field known by other terms, as may be clear to the person skilled in the art. Restriction or limitation if any referred to in the specification, is solely by way of example and understanding the present invention.
As mentioned below, the heart of the process according to the present invention lies in making a health safe, high load bearing structural grade plywood.

The process below describes the manufacturing method of plywood with its relevant machineries.

Timber
Approved species for manufacturing of disclosed Plywood is given below:
1. Gurjan (Dipterocarpus turbinatus)
2. Eucalyptus
Thickness of veneer to be used should be uniform at 1.8 mm ± 0.03 mm.

Peeling
The selected logs are cut as per desired thickness in the peeling process through high speed rotary cut peeling machine. Selected peeled veneers are sorted for any defect and graded accordingly. Minor natural defects are repaired and then forwarded to tenderizing section.

Tenderizing
Tenderizer machine is used to release stress from the veneer resulting in warp free ply. The teeth like structures in the rollers of the machine helps in producing dents minor dents in the veneers which breaks the cells to make it stress free. The dents also helps in effective boding due to more glue absorption.

Drying
The tenderized veneers are then dried to remove excess moisture. The desirable moisture content of veneer after drying is around 8% for BWP grade resin. The dried veneers are then stacked for 24 hrs for stabilization of moisture and conditioning. This helps in having a flat veneer which is required in the next stage of core composing for tight bonding.

Core Composing
The dry veneer is then composed in size of 8ft X 4ft or as per product requirement. The process utilizes advanced cutting of the edges of the veneers to make it 90degrees to the edge so that when joined there is no gap or overlap. The joining is done by hot melt glue which requires high temperature of 140 degrees centigrade to melt and form a layer over the veneers edge. The glue is immediately exposed to cold temperature of 8 degrees centigrade which cooks the glue to form a strong bond between 2 cut veneers. The main advantage of composing is to avoid any core gap or overlapping. This is one of the most advanced machines in manufacturing of improved Fire Retardant Plywood, normally called as Club 5 Hundred.

Panel Making or pre- setting of veneers
Panel could be used in 3 types as given below:
• Taping manually with veneer perforated tapes.
The veneers are cut perpendicular and joint together to form pre-set form of either 8ft X 2ft or 8 ft X 4 ft.

• Full panel
8 ft logs are peeled to get directly 8 ft X 2 ft full panels

• Scarf joint panel.
Veneers are joined longitudinally by butt joint to form longer preset veneers of 8 ft X 2 ft & 8 ft X 4 ft

• Composed panel.
Similar to composed core process, veneers are composed of sizes 4 ft X 4 ft and then scarf joined to form 8 ft X 4 ft panels
The panels are placed along with composed core in alternate layers. As plywood is odd number layered product, the odd layers are called cores and the even layers are called panels. The cores are glued while the panels are non-glued.

Assembling
The construction of a 19mm Fire Retardant Club 5 Hundred base plywood /MAT Plywood is given below
No of Layers ---11
Line No of
Composed Cores Thickness Species
Cores 6 1.8 Eucalyptus
Panels 5 1.8 Gurjan

Glue Spreading
The assembly of MAT ply is done in a 8ft Glue Spreader where the composed cores are passed through the glue spreader so that glue can be passed over it. The panels which are dry are placed on top of the cores alternately. The glue used for spreading is made up of Phenol & Formalin along with bi-flex in glue which kills borers and insects in the ply.
The glue is also added with Tricresyl Phosphate which gives fire retardant property to the plywood.

Pre Pressing
The assembled MAT is then cold pressed in Pre- Press machine where the moisture is uniformly distributed & initial bonding starts. The technical parameters of the pre- press is given below
Specific Pressure -- 16 Kg/cm2
Pressing Time -- 30 mins

Hot Pressing
The glue used is thermosetting which requires heat to polymerize. This is done is a hot press machine. The parameter of the hot press is given below
Specific Pressure ---- 13Kg/cm2
Temperature ---- 1300C +/- 5 0C
Pressing Time of different thickness of improved Fire Retardant Club 5 Hundred MAT
19mm -15mins
16mm-13mins
12mm--10mins
9mm--8mins
6mm--5mins
4mm--5mins

Final MAT quality check is done after unloading from Hot Press. It should be conditioned for 24 hours using humidifier which is an automatic humidity-controlled system.
Calibration
The conditioned MATs are then passed through a Calibrator machine. The machine operates on the principle of sanding both the sides at one go which cuts off any thickness over and above the thickness set in the machine. It has a tolerance of +0.15/-0.15mm. This gives the MAT a smooth finish and a uniform thickness all across both the surface of the MAT.
After the calibration process, each and every sheet is checked, filled with fillers if any natural open pores are found, cooled down and stabilized for 30 minutes before sending to overlaying process.
Till the above process of improved Fire Retardant Plywood called Club 5 Hundred is made only as a base ply or MAT ply which ensures a defect free surface over which final face layer is to be overlaid. Due to the process employed to make the base of Club 5 Hundred ply, it adds the following features in it like zero gap, uniform thickness, even surface, zero warpage . It is to be specially mentioned that due to quality checks after all the processes the final base ply quality is the best.
Overlaying
The base ply is then passed through a 8ft glue spreader where glues is applied on both the surfaces. Similar to how panels were placed in the initial stages, here in the overlaying stage, face veneer is placed on top & bottom of the base ply to give it a uniform looking ply surface. The face also adds strength to the ply.
The glue used for overlaying process is a mix of Melamine with Phenol & Formalin.

Double Pre- Pressing
The overlaid ply is then kept pressed inside a cold press machine for 10 mins where the face slightly clings on to the base ply. The pre pressed ply is then again passed through the same 8 ft glue spreader for a second time and 2 more face veneer is put on the ply. With this the ply is applied with 4 face and 2 glue lines over a base/MAT ply.
In the history of plywood this is a unique process which increases the density as well as the load bearing capacity of the plywood.
The ply is again pressed in the cold press for another 10 minutes and then forwarded for hot pressing.

Hot Pressing
The pre pressed ply is then loaded in a mechanical device called hot press with low temperature (110 degrees centigrade) and high pressure for curing the glue. Hot pressing results in very good bonding of both the face layers with the base ply or MAT ply. The hot pressing time in case of overlaying is fixed at 2.5 minutes for all thicknesses.

Trimming
The size of the plywood is made 1 inch extra on all the 4 sides for initial processing upto overlaying hot pressing. To cut the plywood as per actual size required by the customer, it is trimmed on both length and breadth in a automatic cutting machine.
Sanding
The surface of the face layer is now passed through wide belt sanding machine which sands off the extra fibers of the face to give it a smooth lusters finish.
Preservative Treatment
The sanded plywood is then passed through a warm preservative solution containing Acid Copper Chrome solution. This solution gives anti borer & anti- termite properties to the plywood.
Anti-bacterial Coating
The preservative treated plywood is then coated with an anti-bacterial solution which kills more than 99% bacteria on the surface of the plywood. This ensures a healthy environment for the end users as well as the carpenters who work with the plywood.
Marking & Stamping
The anti-bacterial coated plywood is then finally checked for quality and the good products are then forwarded for marking and stamping as per customer’s requirement.
In an exemplary embodiment, the composition of the anti-bacterial solution is as under:
Constituents % Composition
Silver nanoparticles 1%
Gelatin 1%
2-ethyl hexanol 0.50%
Lauryl alcohol ethoxylate 5%
Cyclic amide 5%
Acrylic Homopolymer 3%
Dipropylene Glycol 12.00%
Water 73%

The anti-bacterial chemical is mixed along with preservative treatment solution to form a homogenous mixture at 60 deg. centigrade. This chemical is absorbed by the plywood as it passes through the dipping solution through an auto conveying tank containing the solution. The solution gets absorbed to an extent of 300 gms per sheet of 8 ft X 4 ft. The antibacterial chemical does not weather. Further, the antibacterial chemical is neutral in nature & is colourless. But, after addition in the preservative solution, it becomes acidic in nature and takes the colour of the preservative solution which is brown in colour.
Results : Contact Time 10 minutes
ANTIBACTERIAL ACTIVITY
1. Test Bacteria : Staphylococcus aureus ATCC 6538
Quantitative Assessment of Activity – JIS Z 2801 : 2010
Untreated : Conc. of inoculum on untreated sample at 0 hours (A) : 1.07 x 105 Log = 5.02
Untreated : Conc. of inoculum on untreated sample after 10 minutes (B) : 1.10 x 105 Log = 5.04
Sample Identification No. Bacteria on treated sample (C) Log of Bacteria on treated sample Antimicrobial
Activity (R) (log B-C) Microbial Kill
(% Reduction)
Control Plywood 8800 3.94 1.10 92.00
Treated Plywood 1000 3.00 2.04 99.09

2. Test Bacteria : Escherichia coli ATCC 8739
Quantitative Assessment of Activity – JIS Z 2801 : 2010
Untreated : Conc. of inoculum on untreated sample at 0 hours (A) : 7.00 x 104 Log = 4.84
Untreated : Conc. of inoculum on untreated sample after 10 minutes (B) : 4.70 x 105 Log = 4.93
Sample Identification No. Bacteria on treated sample (C) Log of Bacteria on treated sample Antimicrobial
Activity (R) (log B-C) Microbial Kill
(% Reduction)
Control Plywood 3800 3.57 1.36 95.63
Treated Plywood 800 2.90 2.03 99.08

The Standard Antimicrobial value of Evaluation R> 2.0
COMMENT :
When tested as specified, Treated Plywood at 10 minutes contact : PASSES the Quantitative Assessment of activity Untreated Plywood at 10 minutes : FAILS the Quantitative Assessment of activity for Staphylococcus aureus and Escherichia Coli by JIS Z 2801 : 2010 Test Method.

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration by way of examples and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. The particular embodiments and •applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims:

1. A process of manufacture of fire retardant and anti-bacterial plywood comprising the steps of :
• Selection of timber
• Peeling of veneer from timber
• Tenderizing the peeled veneers
• Drying the tenderized veneers to achieve upto 8% moisture in the veneers.
• Conditioning of the dried veneers for 24 hrs
• Presetting of veneers through core composing and through panel making
• Assembling with phenol formalin glue
• Cold pressing (pre-pressing) the assembled veneers to form the base ply shape
• Hot pressing the already cold pressed material to make the base ply or MAT ply.
• Calibration of the base/MAT ply to give it a uniform thickness and a smooth top surface for applying face veneer.
• Overlaying with face veneer to put a face veneer on top and bottom.
• Cold pressing the overlaid base ply.
• Overlying second time with 2 more face to give additional strength.
• Again, cold pressing the overlaid ply second time.
• Hot pressing the cold pressed ply
• Trimming the edges of the ply to give it a final cut as per market requirement.
• Sanding the ply to give it a smooth surface
• Dipping the ply in preservative solution for anti-borer and anti-termite property addition
• Giving it a coating of anti-bacteria solution to kill bacteria in the ply; and
• Marking and stamping the final graded product.

2. The process of manufacturing of plywood as claimed in claim 1, wherein the steps of conditioning the veneers for 24 hrs is conditioned to achieve upto 8% moisture content in the veneer and temperature to be that of environment.
3. The process of manufacturing of plywood as claimed in claim 1, wherein the steps of pre setting is done through core composing and making panels by cutting the veneers to required sizes and ensuring perpendicular cuts for ensuring zero gaps & overlap.
4. The process of manufacturing of plywood as claimed in claim 1, wherein the steps of assembling includes addition of Tricresyl Phospahete in glue which ensures that the plywood is given fire retardant properties.
5. The process of manufacturing of plywood as claimed in claim 1, wherein the steps of overlaying two times with 2 faces each time and pre pressing it twice with an additional glue line increases the mechanical properties of the plywood.
6. The process of manufacturing of plywood as claimed in claim 1, wherein the load bearing capacity of the plywood increased almost 20% than a normal structural ply.
7. The process of manufacturing of plywood as claimed in claim 1, wherein the steps of coating includes adding additional layer of anti-bacterial solution after dipping it with preservative solution for making it health safe by killing 99% bacteria in the ply.
8. The process of manufacturing of plywood as claimed in claim 1, wherein the components of the said anti-bacterial chemical solution includes:
Constituents % Composition
Silver nanoparticles 1%
Gelatin 1%
2-ethyl hexanol 0.50%
Lauryl alcohol ethoxylate 5%
Cyclic amide 5%
Acrylic Homopolymer 3%
Dipropylene Glycol 12.00%
Water 73%

9. The process of manufacturing of plywood as claimed in claim 1, wherein the anti-bacterial chemical is mixed along with preservative treatment solution to form a homogenous mixture at 60 deg. centigrade.
10. The process of manufacturing of plywood as claimed in claim 9, wherein the said chemical is absorbed to an extent of 300 gms per sheet of 8 ft X 4 ft by the plywood as it passes through the dipping solution through an auto conveying tank containing the solution.
11. The process of manufacturing of plywood as claimed in claim 9, wherein the antibacterial chemical does not weather, is neutral in nature & is colourless.
12. An anti-bacterial plywood manufactured employing the process as claimed in any of the preceding claims.