SE1651071A1 - Novel laminated veneer lumber product and method of manufacturing thereof - Google Patents

Abstract

The present invention relates to a process for preparing laminated veneer lumber. The invention also relates to a modified laminated veneer lumber product produced using said process.

Description

NOVEL LAI\/IINATED VENEER LUIVIBER PRODUCT AND I\/IETHODFOR IVIANUFACTURING THEREOF Field of the invention The present invention relates to a process for preparing Iaminated veneerlumber. The invention also relates to a modified Iaminated veneer lumber product produced using said process.

Background Traditionally, solid sawn timber is used for wood applications in the outdoors.Tropical hardwood, such as teak (Tectona Grandis), is often used in outdoor applications.

Due to the decreasing availability of stress grading high quality structuraltimber, there is an increasing demand for Iaminated veneer lumber (LVL) toreplace the use of solid wood, particularly in the construction industry.

Laminated veneer lumber (LVL) is a pile of layers or plies of wood veneerbonded one veneer layer to the next by an adhesive. Laminated veneerlumber (LVL) has been developed for structural applications.

LVL for structural applications is generally made from softwood.

LVL made from softwoods is well documented in the art. For example, aspruce LVL has been produced in Finland since 1981 and is known under thename KertoTM. LVL is generally made from softwoods, such as spruce, pineor Douglas fir.

Despite its higher stress design values than solid wood, it is not particularlycommon to use LVL for outdoor usage due to perceived low durability for outdoor usage.

LVL can be subject to dimensional changes and cracks when it is subjectedto moisture and/or environmental changes. These kind of changes can bemore severe in the outdoors, where water, temperature, and humidity areconstantly changing, thus challenging the possibility of using LVL for outdoor USGS.

One of the methods to improve the stability and durability of LVL isimpregnation. This involves the introduction of chemical substances into thewood in order to improve its characteristics and impart new properties.lmpregnation may stabilize dimensions, increase strength, increaseresistance to water and moisture, and reduce cracking. l\/lost impregnation is done directly to a wood lumber via a high pressureprocess. Although theoretically simple, this process presents some difficulties,such as structural collapse, splitting of the wood, and also ensuring therequired transport of actives through the wood.

When applying impregnation to an LVL structure, the impregnation has to beperformed at veneer level, i.e. the chemical should be introduced to eachindividual veneer, each separated by a glue line, which is to form the LVL. Toobtain the desired properties of the LVL, it is essential to ensure efficientimpregnation. Traditionally the impregnation of LVL is similar to other solidwood products, done under high pressure by using C-type copper basedchemical or CC-type chrome-copper based chemicals. However theimpregnation of LVL is much more difficult and time consuming due to the glue lines preventing chemical penetration from single ply to ply.

Phenol-formaldehyde (PF) resins result from the polycondensation of phenoland formaldehyde. From a commercial standpoint, PF resins have been of prime importance since the early 1900”s, when they appeared as the firstsynthetically produced polymers. Empirical research and development hassignificantly contributed to the chemical engineering of PF resin properties. lnfact, PF resin properties can be tailored for a variety of applications, includingfoundry resins, molding compounds and wood-based composite binders. PFresins are weather durable. As a consequence they are utilized in exterior grade wood-based composites.

Adhesive penetration in wood is commonly categorized into gross penetrationand cell wall penetration. Adhesive gross penetration results from the liquidadhesive flowing into the porous structure of wood. For cell wall penetration,the adhesive enters the woody cell wall. Adhesive gross penetration and cellwall penetration are critical to joint performance. l\/lany of the resins used in the art, such as certain commonly used phenol-formaldehyde resins, do not result in LVL with sufficient properties,particularly with regard to resistance to water.

There is thus a need for improved laminated veneer lumber products. Thereis also a need for improved processes for preparing such products.

Summary of the invention lt has been found that many of the chemicals presently used for impregnationhave poor ability to penetrate into the LVL. lt is an object of the present invention to provide a laminated veneer lumberproduct having improved properties, such as improved resistance to moisturepenetration, improved strength and improved termite resistance.

Therefore, one aspect of the present invention is a process for preparinglaminated veneer lumber comprising the steps of a) providing layers of veneer; b) applying a phenol-formaldehyde resin wherein the phenol-formaldehyde has an average molecular weight in the range of from150 g/mol to 300g/mol and a polydispersity in the range of from 1.0 to1.5, on both sides of each veneer; and c) applying 120 to 200 gram per square meter of a high molecular weightphenol-formaldehyde adhesive on at least one side of the veneer fromstep b); and d) curing while pressing the layers of veneer together during heating at atemperature of from 110°C to 130°C. ln one embodiment of the present invention, the amount of phenol-formaldehyde resin used in step b) is in the range of from 1 gram per squaremeter to 20 grams per square meter. ln one embodiment of the present invention, the phenol-formaldehyde resinused in step b) has an average molecular weight in the range of from 150g/mol to 250 g/mol, such as from 150 g/mol to 200 g/mol or from 150 g/mol to190 g/mol or from 150 g/mol to 175 g/mol. ln one embodiment of the presentinvention, the low-molecular weight phenol-formaldehyde resin used in stepb) has a viscosity at 20 °C in the range of from 10 mPa*s to 30 mPa*s, suchas from 15 mPa*s to 25 mPa*s. ln one embodiment of the present invention, the modified phenol-formaldehyde resin is in step b) applied to both sides of each individualveneer simultaneously. ln one embodiment, the phenol-formaldehyde resin is in step b) applied to both sides of each individual veneer using spraying.

One embodiment of the present invention is a laminated veneer lumberproduct obtainable by the process according to the present invention.

Detailed description The low molecular weight phenol-formaldehyde (PF) resin used in step b) inaccordance with the present invention has an average molecular weight offrom 150 to 300 g/mol and a polydispersity of 1 to 1.50. lt is hypothesized thatby using low molecular weight PF with wood material, an intermoiecularcoupiing is enhanced, a behavior ascribed to the low molecular weight PF penetrating lignin on a nanometer scale and polymerizing in-situ.

Resoles result from the polycondensation of phenol with excessformaldehyde in an aqueous alkaline medium. Typically P: F molar ratios liein the 1 :1.1-1:3 range. Metal hydroxides of sodium and potassium arecommonly used as catalysts. Ammonia and tertiary amines such astriethylamines can also catalyze PF condensation. Industrial resoles areusually manufactured by cooking the reagents from 1 to 8 hours attemperatures below 100°C. ln that process water is used as the solvent sothat the final resole solid content lies in the 40 to 60% range.

PF resins achieve their final binding properties as a result of cure. Forresoles, cure is exclusively heat induced and causes changes in thechemistry and in the physical properties of the material. Typically woodproducts are heat and pressure cured at 125-130 °C for 3 min. + 0,5min. xthickness of end product, i.e. 40 mm EWP panel will be cured forapproximately 23 minutes. lf required, the PF resin can be premixed with anti-fungus and/or insect repellant before the composition is used to impregnate the veneers.

According to the present invention, the curing is performed while pressing thelayers of veneer together during heating at a temperature of from 110°C to130 °C.

The amount of phenol-formaldehyde resin used in step b) in the presentinvention ranges of from 1 gram per square meter to 20 grams per squaremeter. The amount can be selected depending on the required properties ofthe product being manufactured. ln one embodiment of the present invention, the phenol-formaldehyde resin isin step b) applied to both sides of each individual veneer simultaneously. lnone embodiment, the phenol-formaldehyde resin is in step b) applied to bothsides of each individual veneer using spraying, brushing or similar. Applyingthe phenol-formaldehyde resin to both sides of the veneer simultaneously isadvantageous in a production setting and increases production efficiency.The applying of the phenol-formaldehyde using spraying can be performedusing equipment and methodologies known in the art.

The high molecular weight PF adhesive used in step c) in accordance withthe present invention is of a type commonly used in the manufacture of LVL.Such high molecular weight PF adhesive typically has an average molecularweight of at least 300 g/mol, such as 500 g/mol, 1000 g/mol or higher. ln oneembodiment, the high molecular weight PF adhesive used in step c) isapplied only on one side of each veneer. ln view of the above detailed description of the present invention, othermodifications and variations will become apparent to those skilled in the art.However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.

Claims (1)

1. Claims A process for preparing a laminated veneer lumber productcomprising the steps of a) providing layers of veneer; b) applying a phenol-formaldehyde resin wherein the phenol-formaldehyde has an average molecular weight in therange of from 150 g/mol to 300 g/mol and a polydispersityin the range of from 1.0 to 1.5, on both sides of eachveneer; and c) applying 120 to 200 gram per square meter of a highmolecular weight phenol-formaldehyde adhesive on atleast one side of the veneer from step b); and d) curing while pressing the layers of veneer together during heating at a temperature of from 110°C to 130°C. A process according to claim 1, wherein the amount of phenol-formaldehyde resin used in step b) is in the range of from 1 gramper square meter to 20 grams per square meter of each side of each layer of veneer. A process according to claim 1 or 2, wherein the phenol-formaldehyde resin used in step b) is applied to both sides of each individual veneer simultaneously. A process according to claim 3, wherein the phenol-formaldehyde resin used in step b) is applied using spraying. A process according to any one of claims 1-4, wherein thephenol-formaldehyde resin used in step b) has an averagemolecular weight of from 150 g/mol to 200 g/ mol. A process according to claim 5, wherein the pheno|-formaldehyderesin used in step b) has an average molecular weight of from150 g/mol to 190 g/ moi. A process according to claim 6, wherein the pheno|-formaldehyderesin used in step b) has an average molecular weight of from150 g/mol to 175 g/ moi. A Iaminated veneer Iumber product obtainable by the processaccording to any one of claims 1-7.