CN109927146B

CN109927146B - Isocyanate adhesive system, method for preparing artificial board by using same and prepared artificial board

Info

Publication number: CN109927146B
Application number: CN201711361405.8A
Authority: CN
Inventors: 李厚义; 涂松; 孙卫华; 张梓军
Original assignee: Wanhua Chemical Group Co Ltd
Current assignee: Wanhua Chemical Group Co Ltd
Priority date: 2017-12-18
Filing date: 2017-12-18
Publication date: 2021-09-07
Anticipated expiration: 2037-12-18
Also published as: CN109927146A

Abstract

The invention discloses an isocyanate adhesive system, a method for preparing an artificial board by using the same and the prepared artificial board. The adhesive system, comprising: (a) polyfunctional isocyanates and acidic compounds; (b) a polyol, an amine catalyst and optionally an iron-containing compound; and optionally (c) an aqueous emulsion. The method comprises the following steps: applying component (a) to the entire substrate, component (b) to the core layer, and component (c) to the skin layer; and then carrying out processes such as paving, hot pressing and the like on the base material to obtain the artificial board. The hot pressing efficiency can be obviously improved, the precuring degree of the adhesive in the wood shavings after glue is applied is reduced, and the utilization rate of the adhesive is improved; can improve the initial viscidity of shaving board blank of colding pressing, solve present PMDI shaving board production, the blank is just viscidity poor, can't pass through the problem in conveyer belt transition clearance. The binder system is particularly suitable for the production of Particle Board (PB) and orientable particle board (OSB).

Description

Isocyanate adhesive system, method for preparing artificial board by using same and prepared artificial board

Technical Field

The invention relates to an isocyanate adhesive system, in particular to an adhesive system for preparing an artificial board and a method for preparing the artificial board by using the same.

Background

The wood or other non-wood plants are used as raw materials, and after the wood or other non-wood plants are mechanically processed and separated into units such as particles, needle-shaped or sheet-shaped shavings, fibers and the like, the wood or other non-wood plants are applied with adhesives or other additives and are hot-pressed to manufacture the artificial boards, and the development is very rapid in recent years. The traditional artificial board products mainly comprise three kinds of boards, namely plywood, shaving board and fiber board, and the extension products or deep processing products of the traditional artificial board products can reach hundreds of kinds. The artificial board is the beginning of the modernization of wood reprocessing, extends from changing the shape of wood to changing the performance of wood, and is a product of the modern industrial progress. The artificial board can improve the utilization rate of wood, save forest resources, and 1 cubic meter of artificial board can replace 3-5 cubic meters of log.

The traditional urea-formaldehyde resin adhesive, phenolic resin adhesive and melamine urea-formaldehyde resin adhesive are all generated by formaldehyde in the using process and finished boards, which pollutes the environment and is harmful to human health.

The novel PMDI (polymethylene polyphenyl isocyanate) adhesive can solve the problem of formaldehyde release, and because the PMDI does not contain a formaldehyde component, the prepared plate is free from artificial addition of formaldehyde release, so that the novel PMDI adhesive is green and environment-friendly; meanwhile, the plate prepared by hot pressing has better water resistance than the plate prepared by urea-formaldehyde glue, and can still meet the requirement of national standard on water absorption expansion rate (the water absorption expansion rate of water bath at 20 ℃ is less than or equal to 8 percent for 2 h) without adding a waterproof agent.

The PMDI is used as an adhesive to prepare the artificial board, the reaction mechanism is that most of functional group-NCO in the PMDI reacts with water in wood or non-wood plant raw materials at high temperature of hot pressing to produce products such as urea (-NH-CO-NH-) and biuret (-NH-CO-N-CO-NH-) and the like, and the products and raw material units generate cementing action to form the artificial board meeting the national standard requirements, and no harmful substances are generated in the whole reaction process. Because the reaction mechanism is different from urea formaldehyde binders, the use of PMDI as the wood binder reaction unit allows for higher moisture content to be retained, which can save costs in the plant wood drying process to some extent.

The hot pressing process involves complex energy changes, including heat and mass transfer processes. The surface layer is preferentially heated, and the water in the unit is heated to be changed into water vapor, and the water vapor carries heat to be transmitted to the core layer. And (3) increasing the temperature of the core layer along with the time, and curing and molding under the action of pressure after the curing temperature of the adhesive is reached. Because the wood material is a poor conductor of heat, the main heat transfer during hot pressing is carried by water vapor. The main factors limiting the efficiency of hot pressing are the slow temperature rise of the core layer and the slow reaction rate of the PMDI binder with water. The most direct performance of improving the productivity is to shorten the hot pressing time, but the core layer adhesive can still be well cured, and the internal bonding strength cannot be obviously reduced; the hot pressing time is kept unchanged, so that the internal bonding strength of the plate can be obviously improved, and the curing rate of the core layer adhesive can also be improved.

The PMDI is used for manufacturing artificial boards, which becomes a new direction for the development of aldehyde-free artificial boards in recent years, and more enterprises begin to produce aldehyde-free artificial boards. Compared with the traditional urea-formaldehyde glue hot-pressing temperature (200-; and because the PMDI glue has no initial viscosity, the adhesion of the pre-pressed plate blank is poor, the plate blank is difficult to pass through a hot press transition conveyor belt on a continuous line, so that the plate blank collapses, the plate forming rate is influenced, and the method is undesirable for enterprises.

After glue is applied to the artificial board structural units, the artificial board structural units are conveyed by a conveyor belt, stored in a storage bin and the like, the activity of isocyanate groups is high, and partial adhesive is cured (pre-cured) at a high workshop temperature, so that the performance of the board is insufficient; the solution generally adopts the increase of the addition amount of the adhesive, which leads to the increase of the production cost.

There is a need for an isocyanate adhesive system for wood-based panels that solves the above technical problems.

Disclosure of Invention

The invention aims to overcome the defects of low efficiency and poor slab adhesion of artificial boards produced by using isocyanate as an adhesive, and provides an isocyanate adhesive system capable of improving the hot pressing efficiency and slab adhesion of artificial boards and a method for preparing artificial boards, so that the hot pressing efficiency of artificial boards is improved on the premise of not changing the original factory production process; meanwhile, the wood shaving aging time can be prolonged, and the pre-curing degree of the adhesive is reduced; the adhesion of the plate blank is improved, and the plate blank is enabled to pass through a hot press conveyor belt transition area in a complete form after being pre-pressed, so that the finished plate has no fracture mark.

In order to solve the technical problems, the invention adopts the following technical scheme:

an isocyanate adhesive system for the production of artificial boards comprising the following components:

(a) polyfunctional isocyanates and acidic compounds;

(b) a polyol, an amine catalyst and optionally an iron-containing compound; and

optionally (c) an aqueous emulsion.

The polyfunctional isocyanate of the present invention includes many kinds, and one or more kinds of the polyfunctional isocyanates may be selected as the main raw material. Isocyanate refers to a compound having an isocyanate (-NCO) group in its structure, and is useful as an adhesive. Polyisocyanates can be divided into four main classes according to the structural features of the connection of isocyanate groups with carbon atoms: aromatic polyisocyanates (e.g., toluene diisocyanate, i.e., TDI), aliphatic polyisocyanates (hexamethylene diisocyanate, i.e., HDI), araliphatic polyisocyanates (i.e., aliphatic hydrocarbon groups, often polymethylene, such as xylylene diisocyanate, i.e., XDI, intercalated between the aryl group and the plurality of isocyanate groups) and cycloaliphatic polyisocyanates (i.e., polyisocyanates bearing a plurality of isocyanate groups on a cycloalkane, such as isophorone diisocyanate, i.e., IPDI). Polyfunctional isocyanates employing any one or a combination of the four broad categories are within the present disclosure. Relatively inexpensive aromatic isocyanates, including Toluene Diisocyanate (TDI), diphenylmethane diisocyanate (MDI) and polymeric diphenylmethane diisocyanate (polymeric MDI or PMDI), are preferred as starting materials. The adhesive widely used in the production of PB and OSB in the artificial board industry is polymeric MDI (diphenylmethane diisocyanate) which is known as polymethylene polyphenyl isocyanate and has the following structural formula:

PMDI is a mixture of polyisocyanates of different functionality where the diisocyanate with n ═ 0 (i.e., MDI) makes up about 40% of the mixture and the MDI structure is dominated by 4,4 '-MDI, possibly with small amounts of the 2, 4' -MDI isomer. Isocyanates whose isomer content is adjusted to give a mass fraction of-NCO of 30-34% are also disclosed. The remainder of the PMDI is a low-polymerization polyisocyanate having a functionality of 3 to 5, the average molecular weight of the PMDI is 320-420, the average functionality is 2.5-3.0, and the viscosity at 25 ℃ is about 150-250 cP.

However, any other modified product based on PMDI or TDI or MDI or a combination product thereof is adopted as the raw material, including but not limited to polyether and polyester modification, the obtained-NCO mass fraction is 20-34%, the viscosity is less than 10000cP at 25 ℃, and the modified product belongs to the multifunctional isocyanate raw material disclosed by the invention. As the main component of the binder system, polymethylene Polyphenylisocyanate (PMDI) having a functionality of 2.6-2.8 and a viscosity of 150-250cP at 25 ℃ is preferred.

The polyol in the component (b) comprises two types of polyether and polyester, forms a soft segment of polyurethane in polyurethane chemistry, has better hydrophilicity, and can improve the hydrophilicity of isocyanate after reacting with-NCO.

Polyester polyols are generally prepared by the condensation (or transesterification) of organic dicarboxylic acids (anhydrides or esters) with polyhydric alcohols (including diols) or by the polymerization of lactones with polyhydric alcohols, the molecular chain of which contains ester linkages (-COO) and terminal hydroxyl groups (-OH). Polyether polyol, also called polyether or polyalkylene oxide, is prepared by ring-opening polymerization of an epoxy compound in the presence of an active hydrogen-containing compound as an initiator and a catalyst. Common epoxy compounds are ethylene oxide, propylene oxide, tetrahydrofuran, and the like. The polyether synthesized by one epoxy compound monomer is called homopolyether, and the polyether synthesized by two or more epoxy compounds is called copolymer. According to the different charging sequence and proportion, random copolymer polyether and block copolymer ether with ordered distribution or disordered distribution can be generated. Hydroxyl-terminated polyether or polyester polyols or mixtures thereof, which may be selected in the described variant, are preferably polyether polyols. The polyether polyols present in embodiments contain primarily primary hydroxyl groups, and may contain minor amounts of secondary hydroxyl groups.

With respect to the polyether polyols used in the present invention, one or more combinations of polyethylene oxide polyols, polypropylene oxide polyols, mixtures of polyethylene oxide and polypropylene oxide polyols, and copolymers thereof; ethylene oxide polyols obtained by ring-opening polymerization of ethylene oxide are preferred. The polyether polyols obtained require, in addition to the epoxy monomer, a catalyst (KOH) and an initiator (polyol or amine) to control the polymerization rate, molecular weight and functionality thereof. The polymerization formula can be represented by the general formula:

wherein YH_nAs starter, polyols (or amines) are generally used, n being the functionality, x the degree of polymerization and R being hydrogen or alkyl. Polyether polyols known from the above formulaHas a functionality equal to that of the initiator; and one initiator molecule generates one polyether polyol macromolecule; methods of adjusting the amount and functionality of the starter may be utilized to control the molecular weight and functionality of the polyether polyol.

The molecular weight of the polyethylene oxide polyol is 8000-200, preferably 5000-800 by adjusting the polymerization degree x.

With respect to polyether polyol functionality, a wide variety of alcohols and amines can be used as initiators for functionality adjustment in the present invention. Initiators include, but are not limited to, those listed such as propylene glycol, butylene glycol, glycerol, trimethylolpropane, ethylenediamine, pentaerythritol, xylitol, diethylenetriamine, sorbitol, bisphenol A, bisphenol S, toluene diamine, and the like. And combinations of these. The present invention may use as initiator a hydrophilic species having a functionality of from 2 to 6, more preferably 3-functionality glycerol or trimethylolpropane or a mixture of both, said weight ratio of polyol in component (b) to polyfunctional isocyanate in component (a) being from 0.01 to 0.2: 1, preferably 0.06-0.12: 1.

The present invention improves the rate of reaction of isocyanate binder with water during hot pressing by adding a small amount of amine compound. In polyurethane chemistry, the catalysts can be divided into two basic classes, one being tertiary amine catalysts and one being metal alkyl compounds. The isocyanate binder system of the present invention selects a small amount of organic tertiary amine as a catalyst to increase the rate of reaction of isocyanate with water. Tertiary amine (R)₃N) is ammonia (NH)₃) The 3 hydrogen atoms of which are substituted by alkyl (R), in combination with the steric and inductive effects of the alkyl, the basic size order of the amine is: secondary amines>Primary amines>Tertiary amines are very weak in basicity. The catalytic action of a tertiary amine is not only related to its basicity, but more importantly is affected by the steric effect of the substituent groups on the tertiary nitrogen atom. The tertiary amine catalyst has better catalytic action on the isocyanate adhesive in the invention and can catalyze the rapid reaction of the isocyanate adhesive and water. Alternative tertiary amine catalysts of the present invention include, but are not limited to, those described below, such as triethylenediamine, triethylenediamineAmines, N-dimethylcyclohexylamine, N-methyldicyclohexylamine, N-methylmorpholine, N-ethylmorpholine, N '-dimethylpiperazine, N' -diethylpiperazine, 1,3, 3-tetramethylpiperidine, bis (2-dimethylaminoethyl) ether, tetramethylbutanediamine, 2,4, 6-tris (dimethylaminomethyl) phenol and the like. The amine catalyst of the present invention can be selected from, but not limited to, one or more of the above listed catalysts, and can be added in an amount of 10000ppm, preferably 1000ppm and 3000ppm, based on the weight of the polyfunctional isocyanate in the component (a).

The isocyanate adhesive system of the invention also relates to an acidic compound additive, which can select gaseous HCl to acidify isocyanate and can also add acyl chloride into the isocyanate. Acyl chloride refers to a compound containing a-C (O) Cl functional group, belongs to the category of acyl halide, and is a carboxylic acid derivative formed by replacing hydroxyl in carboxylic acid with chlorine. The adhesive system is added into an artificial board structure unit, the reaction activity is high at room temperature, and partial reaction can occur when raw materials do not enter a hot press, so that the adhesive is wasted. By adding the acidic compound, the activity of-NCO groups can be reduced, the precuring of the isocyanate adhesive is reduced, and the storage time of raw material units is prolonged. The acyl chlorides selected for use in the present invention include, but are not limited to, the following listed, such as trimethylacetyl chloride, terephthaloyl chloride, adipoyl chloride, isobutyryl chloride, n-octanoyl chloride, and the like. One or more of acyl chlorides are selected as additives, or the multifunctional isocyanate in the component (a) is directly acidified by gaseous HCl, and the acid value of the component (a) after the addition is 10000ppm (calculated as HCl), preferably 3000ppm (500 ppm).

The isocyanate adhesive system of the present invention optionally uses an iron-containing compound as an additive, added to component (b). The iron-containing compound includes any organic or inorganic compound containing iron, and ferrous salt and ferric salt can be selected for addition, including but not limited to the following materials, such as FeCl₂、FeSO₄、FeCl₃、 Fe₂(SO₄)₃、Fe(NO₃)₃Iron acetylacetonate, ferrous lactate and ferric citrateEtc., the invention preferably uses one or more inorganic iron-containing salts as additives, more preferably FeCl₃And/or Fe₂(SO₄)₃As additives, amounts, in terms of iron, of from 20 to 2000ppm, preferably from 200 to 1000ppm, based on the weight of polyfunctional isocyanate in the component (a) may be added.

The isocyanate binder system of the present invention may also contain as component (c) an aqueous emulsion including, but not limited to, PVA (polyvinyl alcohol) emulsions, EVA (ethylene vinyl acetate copolymer) emulsions, PVAc (polyvinyl acetate) emulsions, acrylic emulsions, PUD (aqueous polyurethane) emulsions, and mixtures thereof. The selected water-based emulsion has certain viscosity, and generates a bonding effect under the action of molecular cohesion along with the volatilization of the water of the emulsion.

PVA is white flaky, flocculent or powdery solid, and the physical properties of PVA are influenced by chemical structure, alcoholysis degree and polymerization degree. There are two chemical structures in the polyvinyl alcohol molecule, 1, 3-and 1, 2-glycol structures, but the predominant structure is the 1, 3-glycol structure, the "head-to-tail" structure. The polymerization degree of polyvinyl alcohol is classified into ultra-high polymerization degree (molecular weight 25-30 ten thousand), high polymerization degree (molecular weight 17-22 ten thousand), medium polymerization degree (molecular weight 12-15 ten thousand) and low polymerization degree (2.5-3.5 ten thousand). The alcoholysis degree is generally 78%, 88% and 98%. The alcoholysis degree of partial alcoholysis is generally 87-89%, and the alcoholysis degree of complete alcoholysis is 98-100%. The solubility of polyvinyl alcohol is greatly different according to the alcoholysis degree: the product with alcoholysis degree of 87-89% has the best water solubility, can be quickly dissolved in both cold water and hot water and shows the maximum solubility; the product with alcoholysis degree of more than 90% is generally heated to 60-70 ℃ for complete dissolution; polyvinyl alcohol with alcoholysis degree of more than 99% is only dissolved in hot water at 95 ℃; the product with alcoholysis degree of 75-80% is only soluble in cold water and insoluble in hot water; the alcoholysis degree is less than 66%, and the water solubility is reduced due to the increase of the hydrophobic acetyl content; until the alcoholysis degree is below 50%, the polyvinyl alcohol is not dissolved in water any more.

The EVA emulsion is a high molecular emulsion prepared by using vinyl acetate and ethylene monomers as basic raw materials and copolymerizing the vinyl acetate and ethylene monomers with other auxiliary materials by an emulsion polymerization method, has better toughness and acid and alkali resistance, is the same as PVAc emulsion, and is a common wood adhesive. As for the preparation method of the EVA emulsion, reference may be made to Chinese patent CN106753069A "an adhesive of vinyl acetate and its preparation method" and the document "EVA emulsion production process and market analysis" of Chenmegastone et al. For the preparation method of PVAc emulsion, reference may be made to Chinese patent CN101010347 "Poly (vinyl acetate) emulsion and its preparation method" and "PVAc preparation method and technology" by Truewang et al.

The acrylic emulsion is also a common decorative film forming agent, has certain cohesiveness and has the following preparation mechanism: the vinyl monomer is subjected to emulsion polymerization under the action of an initiator and an emulsifier. The initial stage of the reaction forms a dispersion of the monomers in water, each droplet of the dispersed monomer being the site of the bulk polymerization where reactions such as initiation of the chain, propagation of the chain and termination of the chain take place. As the reaction proceeds, the dispersion of the monomers in water gradually forms a latex. The concrete preparation method can refer to Chinese patent CN106397659A "a high-performance polyacrylic acid latex and its preparation method" and CN107163181A "an acrylic acid emulsion and its preparation method".

PUD refers to an adhesive in which polyurethane is dissolved or dispersed in water, and is also called water-based polyurethane or water-based polyurethane. According to the appearance and the particle size, the waterborne polyurethane is divided into three types: polyurethane aqueous solution (particle diameter <0.001um, transparent appearance), polyurethane dispersion (particle diameter 0.001-0.1um, translucent appearance), polyurethane emulsion (particle diameter >0.1um, white and turbid appearance). But the latter two types are conventionally also referred to collectively as polyurethane emulsions or polyurethane dispersions. The aqueous polyurethane can be classified into anionic aqueous polyurethane, cationic aqueous polyurethane and nonionic aqueous polyurethane according to the charge property of the hydrophilic group. Among them, the anionic type is most important and is classified into a carboxylic acid type and a sulfonic acid type. The waterborne polyurethane can be divided into polyether type, polyester type and polyether and polyester mixed type according to different synthetic monomers. According to the different selected diisocyanate, the waterborne polyurethane can be divided into aromatic and aliphatic, or specifically into TDI type, HDI type and the like. The whole synthesis process of the aqueous polyurethane can be divided into two stages. The first stage is pre-stepwise polymerization, namely, a waterborne polyurethane prepolymer with the relative molecular mass of l000 magnitude is generated by stepwise solution polymerization of oligomer diol, a chain extender, a waterborne monomer and diisocyanate; the second stage is the dispersion of the neutralized prepolymer in water.

The invention can select one or a plurality of aqueous emulsions to be mixed for use, the dosage can be considered according to the practical situation of the wood shavings, the weight ratio of the dosage (solid parts) of the aqueous emulsion to the polyfunctional isocyanate in the component (a) is 0.05-1: 1, preferably 0.1-0.5: 1.

In addition to the main constituents of the isocyanate adhesive system, other types of additives known from polyurethane chemistry, including flame retardants, solvents, mold release agents, colorants, fillers, mold inhibitors, antistatics, antioxidants and light stabilizers, plasticizers, etc., are included in the other compounding agents of the invention. The method of use of these additives may alternatively be added as separate streams, more preferably it is added as a batch into both streams (b) and/or (c) as described above.

The invention also provides a preparation method of the artificial board, which comprises the following steps:

(1) providing a substrate comprising wood or non-wood particles, shavings, which meet production requirements;

the base material comprises a plurality of raw material components, can be conventional wood, including wood particles and wood shavings produced by crushing poplar, pine, eucalyptus and the like, and can also be wood particles processed by non-wood units such as wheat, rice, bagasse, cotton stalks, reeds and the like. In a preferred embodiment, the substrate selected is a lignocellulosic material, most preferably a raw substrate for producing particle board or oriented strand board;

(2) the invention provides an isocyanate adhesive system, which comprises polyfunctional isocyanate, an acidic compound, polyol, an amine catalyst, an optional iron-containing compound and an optional aqueous emulsion. Wherein the adhesive system is formulated into a plurality of separate streams, wherein: one stream comprises (a) a polyfunctional isocyanate and an acidic compound; the second stream comprises (b) a polyol, an amine catalyst, and optionally an iron-containing compound; if an aqueous emulsion (c) is used, the third stream comprises the aqueous emulsion (c);

(3) uniformly adding the plurality of separate streams, without premixing, to the substrate in a form sufficient for sizing;

in a preferred embodiment of the method, the plurality of separate streams are applied to the synthetic board substrate. Each separate stream may be added using rotary atomization or high pressure atomization or a combination of both; the adding place is selected to be a closed roller capable of completing stirring and mixing, so that the corresponding material flow is more uniformly mixed with the artificial board base material unit. More preferably, the first material flow is applied to the whole base material, the second material flow is applied to the core layer, and the first material flow and the second material flow can be added after being mixed according to the weight ratio of the second material flow to the water of 1:1 to 1:5, so that the dispersion uniformity is improved; if a third stream is used, the third stream is preferably applied to the surface layer and may be added after mixing in a weight ratio of the third stream to water of from 1:1 to 1:5 to improve the uniformity of dispersion;

(4) and (4) carrying out technical processes of paving, hot pressing and the like on the base material obtained in the step (3) to obtain the artificial board.

Preferably, the artificial board base material unit added with the adhesive system is subjected to layered paving to manufacture boards. When the device is operated in a laboratory, the bottom layer material is paved on the metal base plate processed by the release agent, and is limited by the box body die with the limited size, so that the redundant material is prevented from scattering at the edge. After the adhesive is applied, the paving process should be carried out at a low temperature as much as possible. The longer the time the substrate and adhesive system are in full contact and exposed to air prior to pressing, the greater the degree of isocyanate pre-cure, directly resulting in a reduction in the adhesive available to bond the substrate and a reduction in the mechanical properties of the formed panel. Since each process of the sheet making operation requires a certain time, the hot pressing is preferably performed within 2 hours, more preferably within 1 hour, and further preferably within 0.5 hour after the sizing. The acid compound additive can properly reduce the pre-curing degree of the adhesive, and the mechanical property of the board is not remarkably reduced within 0.5 hour after the wood shaving base material is applied with the adhesive.

In industrial production, a base material unit is paved by using a paving head or a paving roller, a plate blank needs to be pre-pressed before entering a hot press, the plate structure is relatively compact, a certain thickness is maintained, and the plate blank enters the hot press, and the plate blank can maintain a complete shape without collapse and scattering due to the addition of the aqueous emulsion. The longer the hot pressing time, the better the mechanical properties of the formed sheet, since the adhesive is fully cured; however, the long hot pressing time leads to a reduction in production efficiency, which is undesirable for the enterprise. By adopting the adhesive system, the hot pressing time can be properly reduced to improve the production efficiency, the production efficiency can be improved by more than 15 percent, and great benefit is brought to factories.

And (3) cutting the rough edges of the plate blank after hot pressing, cutting the plate blank into a fixed size according to requirements, carrying out aging treatment, and carrying out subsequent treatment such as sanding and veneering to obtain a final product.

The adhesive system comprises polyfunctional isocyanate, polyol, an amine catalyst, an acidic compound, an optional iron-containing compound and a water-based emulsion, and can reduce the precuring of the adhesive at room temperature, thereby achieving the purposes of reducing the cost and improving the production efficiency; meanwhile, the adhesion of the pre-pressed plate blank is improved, no collapse and scattering in the production process of the plate are ensured, and the finished plate has no fracture.

Drawings

Fig. 1,2 and 3 are transition sectional views of cold pressed slabs of examples 12 and 13 and comparative example 5, respectively.

The specific implementation mode is as follows:

embodiments of the present invention are further illustrated by the following examples, but the present invention is not limited to the examples listed, and is intended to include any other known variations within the scope of the invention as claimed.

Polymethylene polyphenyl isocyanate (PMDI): a functionality of about 2.7, a viscosity of 180-250cP at 25 deg.C, an-NCO content of 30.5-32%, Vanhua chemical group, Inc.;

polyether polyol: polyethylene oxide polyol, number average molecular weight 800, initiated by glycerol, with a functionality of 3, warfarin; polyethylene oxide polyol, number average molecular weight 5000, initiated by glycerol, with a functionality of 3, warfarin;

aqueous emulsion: acrylic emulsion, Archsol 8016, solids content 52%, wanhua chemical group limited; EVA emulsion, DA102, solid content 55%, Dajunhua chemical industry (Jiangsu) Co.Ltd;

mold release agent, PAT-7399/C, Germany Huoshi company;

wood raw material, surface core layer raw material for particle board, water content about 3 wt%, poplar, self-made.

Example 1:

the component (a) adopts PMDI, terephthaloyl chloride is added, and the acid value of the PMDI (calculated as HCl) is adjusted to 500 ppm; the component (b) is polyether polyol with the number average molecular weight of 800, triethylene diamine is added, the addition amount is 1000ppm, and FeCl is added₃An addition amount (in terms of Fe) of 200ppm (1 part by mass of PMDI); the glue application amount is the dry weight ratio of the wood shavings.

Preparing a shaving board:

the wood shavings with certain mass are led into a sealing cylinder with stirring equipment, and materials are added in a high-pressure atomization mode. The rate of addition of component (a) was controlled at 1g/s and component (b) was diluted with 5 times the mass of water at 1g/s to ensure uniform application of the binder component to the strands. The addition is carried out in such a way that component (a) is added to the surface core strands and component (b) is added only to the core strands. The surface layer shaving water content is 11.75 wt%, and the core layer shaving water content is 8.59 wt%.

Placing a 50X 50cm stainless steel metal base plate into a hot press for preheating, spraying a demolding agent, and paving a shaving board in a 35X 35cm box body die in a manual paving mode, wherein the paving proportion of a surface core layer is 1: 3: 1. And (5) hot pressing after paving, wherein the thickness gauge is 18 mm. The hot pressing process adopts 3-stage pressure, which is divided into three stages of high, middle and low, and the pressure maintaining time ratio is 4: 4: 3, the hot pressing factor is 6s/mm, and the hot pressing temperature is 220 ℃.

After hot pressing, the wood is placed at room temperature for 2-3 hours, the density of the board is tested after cutting, and the internal bonding strength (IB), the surface bonding Strength (SB), the elastic Modulus (MOE), the static bending Modulus (MOR) and the 2-hour water absorption expansion rate (2h-TS) are tested according to the national standard GBT 17657 and 2013 artificial board and artificial veneer physical and chemical property test method.

The specific parameters for the plate are shown in Table 1, and the properties of the plate are shown in Table 2.

Examples 2 to 6

The kind of the raw material of the embodiment 2 or 6 is the same as that of the embodiment 1; in the embodiment 3, the molecular weight of the polyether polyol is 5000, and the types of the other raw materials are the same as those in the embodiment 1; fe was used as the iron salt of component (b) in example 4₂(SO₄)₃The amount of the Fe used was 1000ppm (1 part by mass of PMDI), and the types of the other raw materials were the same as in example 1; in example 5, tetramethylbutanediamine was used as the amine catalyst of component (b), and the amount of the added tetramethylbutanediamine was 3000ppm, and the kinds of the other raw materials were the same as those in example 1. The specific parameters are shown in Table 1, and the properties of the plate are shown in Table 2.

Comparative examples 1 to 2

Comparative example 1 no component (b) was added to the core layer; comparative example 2 component (b) was not supplemented with iron salt, and the corresponding board-making parameters are shown in table 1, while the rest refer to example 1, and the board properties are shown in table 2.

TABLE 1 specific parameters of the sheet

TABLE 2 sheet Properties

	IB/Mpa	SB/Mpa	MOE/Mpa	MOR/Mpa	2h-TS
						Example 1	0.57	0.92	2616	16.38	3.83％
Example 2	0.60	0.94	2754	16.95	3.94％
						Example 3	0.56	0.91	2742	16.35	3.77％
Example 4	0.61	0.89	2712	16.23	3.89％
						Example 5	0.62	0.93	2679	16.42	4.11％
Example 6	0.44	0.90	2456	16.11	4.03％
						Comparative example 1	0.45	0.95	2535	16.21	3.52％
Comparative example 2	0.53	0.91	2589	16.25	3.88％

As can be seen from Table 2, the performance of the boards prepared by the selected examples meets the requirements of the national standard on the performance indexes of the shaving boards. Under the condition of the same hot pressing factor, the raw materials of the examples 1 to 2 are the same in type, and the comparative examples 1 and 2 show that the addition amount of the component (b) is increased from 0.18 percent to 0.36 percent of the content of the wood shavings, the improvement of the performance of the plate is small, and the use amount of the component (b) is in a proper level.

Compared with the comparative example 1, in the examples 1-5 in which the component (b) is added to the core layer wood shavings, the bonding performance in the plate is obviously improved under the condition of the same hot pressing factor, the material selected in the example can improve the performance of the plate, and the effects are approximately the same. The internal bonding performance is the most critical factor for restricting the production efficiency, and the improvement of the internal bonding performance of the plate directly indicates that the curing rate of the core layer adhesive is improved, so that the hot pressing time can be reduced to improve the production efficiency.

Comparing the comparative example 1 with the example 6, it can be found that after the polyol component is added to the core layer, under the condition of reducing the hot pressing time (from the hot pressing factor of 6s/mm to 5s/mm), the internal bonding performance of the board is still not significantly reduced, which indicates that the isocyanate adhesive system provided by the invention can reduce the hot pressing time and improve the hot pressing efficiency by about 16%.

Example 1 compared with comparative example 2, because example 1 adds more FeCl₃The internal bond strength is improved by about 7.5% compared to comparative example 2, indicating that FeCl₃The addition of (2) can improve the curing degree of the adhesive, thereby indirectly indicating that the production efficiency can be improved.

Examples 7 to 11

An aging link is added before pavement, namely after glue is applied, the wood shaving units are sealed and aged for a certain time and then are paved, the aging temperature is 50 ℃, and the hot pressing factors are all 6 s/mm. The raw materials of examples 7 to 9 were the same as those of example 1, and the acid value of PMDI in examples 8 to 9 was 3000 ppm; examples 10 and 11 PMDI was acidified with isobutyryl chloride to an acid value of 500ppm, other board making parameters are shown in table 3, the remaining process conditions are referenced to example 1 and board properties are shown in table 4.

Comparative examples 3 to 4

The corresponding specific parameters for the plate making of comparative example 3 or 4 are shown in Table 3, the rest of the process conditions refer to examples 7-11, and the plate properties are shown in Table 4.

TABLE 3 specific parameters of the sheets

TABLE 4 sheet Properties

The pre-curing degree of the adhesive is researched and mainly reflects the mechanical property of the finished plate, the pre-curing amount of the adhesive is small, and the performance of the plate prepared by hot pressing is improved. As can be seen from the variation trends of IB and SB in Table 4, the performance of the plate is significantly lower after being sealed and aged for 1h at 50 ℃. The IB/SB reduction ratio is combined, so that the performance of the comparative examples 3-4 without the acid compound is reduced more remarkably. The board prepared by adding different types of acidic compounds and PMDI with different acid values has smaller performance variation difference, which shows that the addition of the acidic compounds can inhibit the pre-curing degree of an isocyanate adhesive system and improve the utilization rate of the adhesive.

It can be seen from the above examples 1 to 11 and comparative examples 1 to 4 that the isocyanate adhesive system of the present invention can improve the production efficiency of the artificial board and reduce the pre-curing degree of the adhesive without increasing the amount of the isocyanate adhesive.

Example 12

Adding 3 times of water by mass into acrylic acid water-based emulsion (with solid content of 52%), diluting, atomizing, gluing into surface layer wood shaving particles, cold pressing the plate blank after gluing, simulating continuous line prepressing, compressing the plate blank to about 35cm under the same condition, maintaining the pressure for 5-6S, taking out, and placing on a simulation transition machine for conveyor belt transition simulation. The simulated slab transition equipment was adjusted according to the parameters provided by difenbach, the belt speed after adjustment was about 230-.

Example 13

Example 13 uses an EVA emulsion (55% solids) and the rest refers to example 12, the corresponding plate-making parameters are shown in Table 5.

Comparative example 5

Comparative example 5 the addition of component (c) was omitted and the remainder was carried out with reference to example 12, the corresponding plate-making parameters being shown in Table 5.

TABLE 5 specific parameters of the sheets

Solid parts of component (c).

During the test, the photographs were taken at the transition of the conveyor belt, see figures 1,2, 3.

The slabs of examples 12 and 13 maintained a relatively intact morphology as they passed through the gap between adjacent belts, and the slabs did not fall apart, collapse and break during passage through the gap, indicating that the slabs had better initial tack after addition of component (c). In comparative example 5, since component (c) was not added, when the slab passed through the gap of the conveyor under the same conditions, the slab had no initial tack and collapsed and scattered at the gap, which resulted in failure of normal production of the subsequent plate.

Finally, it should be noted that the above-mentioned embodiments only illustrate the preferred embodiments of the present invention, and do not limit the scope of the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that various changes and modifications can be made by modifying the technical solution of the present invention or equivalent substitutions within the scope of the present invention defined by the claims.

Claims

1. A method of making an artificial board comprising the steps of: (1) applying component (a) a polyfunctional isocyanate and an acidic compound to the entire substrate, applying component (b) a polyol, an amine catalyst and an iron-containing compound to the core layer, and optionally applying component (c) an aqueous emulsion to the skin layer;

(2) paving the base material obtained in the step (1) and hot-pressing.

2. The method of claim 1, wherein the polyfunctional isocyanate is selected from one or more of an aromatic polyisocyanate, an aliphatic polyisocyanate, an araliphatic polyisocyanate, and a cycloaliphatic polyisocyanate.

3. The method of claim 1, wherein the polyfunctional isocyanate is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate and polymethylene polyphenyl isocyanates.

4. The method of claim 1, wherein the acidic compound comprises HCl and/or acid chloride; the acyl chloride comprises one or more of trimethyl acetyl chloride, terephthaloyl chloride, adipoyl chloride, isobutyryl chloride and n-octanoyl chloride; the amount of the acidic compound used was 10000ppm in terms of the acid value of component (a) after addition of the acidic compound in terms of HCl.

5. The process as claimed in claim 4, wherein the acidic compound is used in an amount of 500-3000ppm in terms of the acid value of component (a) after addition of the acidic compound, calculated as HCl.

6. The method of claim 1, wherein the polyol comprises one or more of a polyether polyol and a polyester polyol;

the weight ratio of the polyol in the component (b) to the polyfunctional isocyanate in the component (a) is 0.01-0.2: 1.

7. the method of claim 1 wherein the polyol comprises a polyethylene oxide polyol having a functionality of 2-6 number average molecular weight of 200-8000;

the weight ratio of the polyol in the component (b) to the polyfunctional isocyanate in the component (a) is 0.06-0.12: 1.

8. The method of claim 1, wherein the polyol comprises a polyethylene oxide polyol having a functionality of 3 and a number average molecular weight of 800-.

9. The method of claim 1, wherein the iron-containing compound comprises one or more of a ferrous salt and a ferric salt.

10. The method of claim 1, wherein the iron-containing compound comprises FeCl₂、FeSO₄、FeCl₃、Fe₂(SO₄)₃、Fe(NO₃)₃One or more of ferric acetylacetonate, ferrous lactate and ferric citrate.

11. The method of claim 1, wherein the iron-containing compound comprises FeCl₃And/or Fe₂(SO₄)₃。

12. The process of claim 1, wherein the iron-containing compound is used in an amount of 20 to 2000ppm, based on iron, based on the weight of the polyfunctional isocyanate in component (a).

13. The process of claim 1, wherein the iron-containing compound is used in an amount of 200-1000ppm, calculated as iron, based on the weight of polyfunctional isocyanate in component (a).

14. The method of claim 1, wherein the aqueous emulsion comprises one or more of a PVA emulsion, an EVA emulsion, a PVAc emulsion, an acrylic emulsion, and a PUD emulsion.

15. The process of claim 1 wherein the aqueous emulsion is used in a weight ratio of the amount of the polyfunctional isocyanate in component (a) on a solids basis of from 0.05 to 1: 1.

16. the process of claim 1 wherein the aqueous emulsion is used in a weight ratio of 0.1 to 0.5:1 parts by solids to polyfunctional isocyanate in component (a).

17. The method according to claim 1, wherein component (b) and water are applied to the core layer after mixing in a weight ratio of 1:1 to 1: 5;

the component (c) and water are mixed in a weight ratio of 1:1 to 1:5 and applied to the surface layer.

18. An artificial board made according to the method of any of claims 1-17.