HPL Plywood (Made In China ,USA , Israel )
Some of the details were edited by me ,according to China HPL production Process and related technology .
1. High pressure laminates – Production process
2. Raw materials
3. Resin production
4. The impregnation (treating) of papers
5. Assembling and build-up
6. The high pressure process
7. Trimming, Sanding, Inspection
A lot of famous brand names ,such as Formica, Arborite, Micarta, Consoweld, Alpikord, Duropal,Weideda ,Tianrun,zhenghang and yongwei .In China ,Mostly are from Yongqiao ,Changzhou city ,and Henan Yongwei ,very few from Linyi area .
HPL is the short name of High Pressure Laminate ,are made from specially selected kraft paper and printed decorative papers impregnated with thermosetting synthetic resins and fused together under heat and high-pressure in a controlled environment to form single high-density sheets of laminates.
The surfaces patterns ( textures and finishes) and colours on the laminates are impregnated with melamine-based resins to provide higher resistance against abrasion, shock and impact, heat, and discolouration.
Let’s start the talking from the high pressure laminates Manufacturing process ,you can understand better what is the real HPL .
Raw materials used for making the HPL : 1.Krart paper ,2.decorative paper ,3 Overlay paper, 4.Phenolic /MElamine Glue
- Overlay paper, which serves to improve the abrasion, scratch and heat-resistance
- Decorative paper, which defines the design and is composed of colored or printed paper
- Kraft paper, which is used as core material and control product thickness.
The thermal lamination is the irreversible process which gives origin to the HPL: the impregnated sheets of decorative and kraft paper undergo a simultaneous pressing and heatingprocess at high levels of heat and pressure.
Impregnation. In the HPL production process, the impregnation is the operation of preparation of the kraft and decorative papers. They are first soaked (impregnated) in thermosetting resins, then dried. The paper so prepared will give origin to the HPL sheet during the thermo-lamination process.
High Pressure Laminate or HPL, is the direct descendent of the original plastic laminate. It is considered to be one of the most durable decorative surface materials and is available with special performance properties including chemical, fire and wear resistance. Special grades of HPL can be postformed around curved edges by application of heat and restraint.
HPL is produced by saturating multiple layers of kraft paper with phenolic resin. A layer of printed décor paper is placed on top of the kraft paper before pressing. The resulting sandwich is fused together under heat and pressure. Because phenolic and melamine resins are thermoset plastics, the curing process transforms the resin into plastic by a cross linking process that converts the paper sheets into a single, rigid laminated sheet. Thermosetting creates strong, irreversible bonds that contribute to its durability.
High pressure laminate is laminated to a composite panel utilizing a variety of adhesives. Particleboard or MDF are the preferred substrate because they provide a stable, durable, consistent and economical foundation. Due to its durability, high pressure laminates are a common choice for horizontal surfaces including flooring, countertops and desktops.
After the papers are impregnated with the resins, the three layers of paper/resin are placed into a press which simultaneously applies heat and pressure . The pressing operation allows the thermoset resins to flow into the paper, then subsequently cure into a consolidated sheet with a density . During the press cycle, the decorative surface can also be cured while in contact with a textured surface to create one of many different surface finishes.
HPL consists of more than 60 to 70% paper, with the remaining 30 to 40% a combination of phenol-formaldehyde resin for the core layers and melamine-formaldehyde resin for the surface layer. Both resins belong to a class of thermosetting resins which crosslink during the press cycle creating irreversible chemical bonds that produce a nonreactive, stable material with characteristics different and superior to those of the component parts.
HPL can be produced using both continuous and discontinuous (batch) manufacturing processes. HPL are supplied in sheet form in a variety of sizes, thicknesses and surface finishes.
High pressure laminates – Production process
High-pressure decorative laminate(s) (HPL)
Sheet(s) consisting of decorative surface layer(s) and core layers bonded together by a high pressure Process. Typical values for the high pressure process are a temperature of ≥ 120 °C and a pressure of ≥ 5 MPa.
upper decorative layer consisting in one or more sheets of fibrous material (usually paper) impregnated with aminoplastic thermosetting resins (usually melamine based resins) or other curable resins or other decorative design surfaces such as metal foils, wood-veneers and textiles, etc. which are not necessarily treated with thermosetting resin The surface layers can appear on one or both side(s) of the laminate(s). In case of one-sided laminates, the back of the sheet(s) may be made suitable for adhesive bonding to a substrate.
Core layer consisting of fibrous materials (usually paper) impregnated with thermosetting resins (usually phenolic based resins) or other curable resins, eventually reinforced by metal layer(s) or metal mesh(es) and others which are not necessarily treated with thermosetting resin.
Saturating Kraft paper for HPL has absorption capacity suitable for resins. Kraft paper may be made of virgin and/or recycled fibres.
Decor paper is bleached and pigmented paper providing an aesthetically pleasing appearance. The decorative layers can be pigmented solid colours or more unique patterns using gravure roll or digital printing technologies such as wood grains, stone patterns and individual designs.
Overlay is a bleached unpigmented, transparent paper with very high absorption capacity for resins. It is used to improve abrasion resistance.
Melamine resins are made from melamine and formaldehyde solution. Melamine resins are transparent, lightfast, scratch resistant, hard coatings best applicable for the surface layers of HPL.
Phenolic resins are made from phenol and formaldehyde solution. Phenolic resins are brownish,relative elastic compounds for the core layers of HPL.
Both resins are produced in a batch process. In kettles the chemical components react together under well controlled conditions. Formaldehyd connects to melamine molecules or phenol molecules and forms reactive compounds for the further impregnation and press process.
The impregnation (treating) of papers
Kraft paper and decor paper are delivered in large rolls. In continuous horizontal “treaters” (i.e. impregnation machines) the paper is unwound, immersed into the resin bath, saturated with resin and then dried. The dry paper, filled with still reactive resin, is cut to sheets of the desired length or wound up again and stored in conditioned rooms for later use.
Assembling and build-up
The treated papers are collected from stock and assembled in clean, dust free rooms to build the right order in the desired colour, size, thickness and backing:
Typical build-up of a HPL
Single sided laminates are always produced “back to back”, using a release paper. Release papers (i.e. coated special papers) or foils are applied to avoid sticking of laminates together in the press. In case of multi-opening-presses (multi-daylight-presses) the assembling must be repeated many times to fill the press. Presses with up to 45 openings are in use. Every opening is filled with up to 24 single sided laminates (usually 0.5 – 1.9 mm thick) or at least with one compact laminate (usually 2 to 20 mm thick).
The high pressure process
Multi-daylight presses are loaded at room temperature, closed, set under hydraulic pressure and heated up to more than 120 °C. The heat causes a liquefying process of the melamineand phenolic resins. At high pressure the liquid resins are pressed between and into the cellulosic
fibres – the density increases followed by the completion of the chemical reaction (polycondensation), called “curing”. That forms a homogenous rigid, completely cross-linked network in the form of the sheet. The result is a non-porous laminate, which will not melt. The cellulose fibres reinforce the laminate. They are chemically bonded and fully integrated into the new compound. The structure of the surface (high gloss, matt, textured etc.) is formed by the press plate (or templates) pressed against the liquefied and afterwards cured melamine layer. After curing is completed, the laminates is cooled down under pressure to release any tensions. The complete press cycle may take up to 100 min. depending on press load and max. temperature.
Trimming, Sanding, Inspection
The laminates are unloaded from the press, and any release material is stripped off. The length and width of the laminate are cut to the required size. Single sided laminates are sanded on the back to improve gluing. After surface and quality inspection for defects the laminates are labelled, packed and stored for further disposition.
Fabrication of HPL elements and compact sheets
Single-sided laminates are usually glued to substrates (e.g. chipboard, MDF etc.) to obtain composite elements.
Edging strips may be applied or the laminate may be postformed (e.g. for kitchen worktops).
Compact laminates are cut to size, and fittings are attached to make them ready to be installed as lockers, cubicles, partition-walls, etc
The rolls of kraft paper and decorative paper are first put on enormous unwinders, unwound and treated (impregnation in liquid resin bath followed by oven drying and cutting to a defined size).
The kraft paper used for the core of the panels is impregnated with phenolic thermosetting resins, whereas the decorative paper used for the surface is treated with thermosetting melamine resins. This decorative paper (which is made mainly of pigments and/or inks and cellulose pulp) is specifically designed so that it can maintain high levels of resistance to sunlight radiation (including UV rays, visible rays and IR), thus ensuring a good colourfastness.
Kraft paper sheets are stacked up and joined to the decorative paper to make a panel of a specified thickness. Approximately 50 sheets of kraft paper and at least two sheets of decorative paper are needed to make a standard panel (double sided) with nominal thickness of 10 mm.
The stack-up of impregnated sheets are placed into multi-daylight presses and subjected to the simultaneous application of heat and pressure . The polycondensation reaction takes place leading to the formation of chemical cross-linking structure where both the phenolic and the melamine resins are firmly chemically bonded together.
The panels produced this way are then trimmed and subjected to a final inspection, so that later are ready to be shipped.
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