FI63542B - FRAMSTAELLNING AV BELAGD PRODUCT FOERSEDD MED EN FENOLFORMALDEHYDBARRIAER MOT POLYISOCYANATBINDEMEDEL - Google Patents

Description

T2EμΠ r & l «« ANNOUNCEMENT s-7 r Λ r, jpjjfo ^ ^ UTLACGNI NGSSKRIFT 6 3 5 4 2 ^ Patent: .ddelot ^ * '(51) Kv.ik? /IBt.a.3 B 32 B 33/00 ENGLISH —Fl N LAND (li) hMmMMm — intact imim 762787 (22) H «k * mhpilvl — AmMcnlitgidag 30.09-76 '(23) Alkupllvft — GlMghMdag 30.09.76 (41) Tullut (ulklMkd - Bltvk affmtNg 09 OU 77 rumaa. . rrtlrtfllfllltu.

Patent- och ragictaratyralaan '7 AimWom uti «* d och wi. * Krtft * n pwMicmd 31.03.83 (32) (33) (31) Holy MuolkMit — B * gtrd prior ** 08.10.75 USA (US) 620850 (Tl ) Ellingson Timber Co. , 3275 Baker Street, Baker, Oregon, USA (72) Philip Duane Shoemaker, Baker, Oregon, Hobert Owsley McQueary,

The present invention relates generally to an inner layer of particulate cellulosic material and an associated coating.

Many shaped articles are made by a basic process in which a cellulosic material is reinforced or bonded together using pressure, heat and a chemical binder. These include wood-based products such as plywood, hardboard, particle board, plywood-coated particle board, and compressed products made from vegetable fibers such as corn stalks, straw, bagasse, or other cellulosic material such as pulp or paper strips. Typically, the adhesives and binders used in the manufacture of such products are thermosetting resins such as phenol formaldehyde, resorcinol formaldehyde, melamine formaldehyde, urea formaldehyde, urea furfural and condensed furfuryl alcohol resins.

In recent years, attempts have been made to use organic polyisocyanate as a binder in the manufacture of reinforcement products. The polyisocyanate, which in most cases 2,63542 is in the form of a liquid and sometimes a dry powder, and the cellulosic material are mixed as a production raw material. Using heat and pressure, the finely divided material is bound into a solid body. The product thus prepared has good strength and weather resistance properties, but unfortunately the tendency of the isocyanates to adhere to the metal can cause difficult adhesion problems in the compression step, mainly in fiberboard manufacturing.

For example, in the manufacture of a plywood-coated particle board product, when polyisocyanate is used as a binder, this tends to penetrate the plywood during compression and adhere to the film sheets of the press. As a result, the product adheres to the film sheet after pressing, unless special release agents are used.

The present invention provides a process for the manufacture of a reinforcement product which has been found to almost completely eliminate the adhesion normally associated with the use of a polyisocyanate binder and which can be used to produce a very high quality sheet with particularly good strength, weather resistance and aging properties.

Thus, the invention relates to a process for producing a coated product, in which a sheet-like coating with a phenol-formaldehyde resin film on one side is applied to a porous base formed by a layer of fine, loose cellulosic material and a binder mixed therewith containing at least an organic polyisocyanate. The method according to the invention is characterized in that the resin film side of the coating is placed against the porous base and the coating and the cellulosic material of the porous base are combined into one entity using heat and pressure in a manner known per se. The method creates an excellent bond between the coating and the inner layer, which is probably due in part to a chemical reaction that takes place between the free hydroxyl groups of the isocyanate and the phenolic resin of the raw material which is converted into the inner layer. In addition, the phenol formaldehyde resin condenses in the compression step and a barrier layer is formed which prevents the polyisocyanate in the raw material from penetrating the coating and further onto the surface of the press film sheet. When polyisocyanate is used as a binder for the cellulosic material forming the inner layer, very little water vapor is formed in the inner layer, which removes e.g. blistering problems normally encountered in the manufacture of coated products. The rebound in the inner layer or the tendency of the inner layer to expand after compression 63542 are insignificant. The conditions can be arranged so that the post-polymerization or polymerization of the binder in the inner layer after compression, which takes place as an exothermic reaction when the raw materials contain a phenolic resin binder, is insignificant.

The invention is particularly suitable for the production of coated products in which the coating is a water-permeable sheet, e.g. a paper sheet. In this case, it has been quite surprisingly found that when the coating is paper, excellent results are obtained by wetting the paper before pressing the raw material and the paper coating. It is obvious that due to such wetting, the polymerization of the phenol-formaldehyde resin binding the coating and the inner layer is slowed down to such an extent that the pressure of the press causes optimal contact between the paper and the raw cellulosic material. The heat of the press evaporates the water in the paper, which eventually escapes through the paper and to some extent plasticizes the raw material from the cellulosic material. An excellent product is formed that is very well suited for outdoor use and at the same time excellent adhesion control to the film sheets is achieved.

The invention has advantages when used in connection with other types of coverings, e.g. plywood coverings. Various phenol-formaldehyde resin layers can be used in the invention as a coating binder, e.g. resin binders and so-called sheet adhesive (which is a resin on a cellulose support).

The invention further relates to a process for the preparation of a coated product using water-permeable coatings, e.g. sheets of paper, which are almost completely impregnated with water before pressing and reinforcement.

The objects of the invention and the advantages achieved by it are described in more detail in connection with the examples.

In carrying out the present invention, a binder system consisting of an organic polyisocyanate and formaldehyde can be used in the production of the cellulose raw material. For example, it has been found that such a binder can be used to produce products with excellent strength and moisture resistance, and cellulose starting materials with a relatively high moisture content can be used in the production of the raw material, i. Up to 22 #. In many cases, this eliminates the need to pre-dry the cellulosic material.

The polyisocyanate component of the binder system may be any organic polyisocyanate having at least two active isocyanate groups in the molecule or a mixture of such compounds. Useful polyisocyanates include diphenylmethane diisocyanates, m- and p-phenylene diisocyanates, chlorophenylene diisocyanates, toluene diis and triisocyanates, triphenylmethane triisocyanates and diphenyl ether tri-2'-isopropyl ether. Particularly suitable are polyphenyl polyisocyanates, e.g. diphenylmethane-U, U * -diisocyanate. Polyisocyanate blends can also be used, e.g., "PAPI", a commercial, approximately trifunctional polymethylene polyphenol isocyanate manufactured by the Upjohn Company, Polymer Chemicals Division.

At ordinary temperatures, formaldehyde is a gas. Therefore, the formaldehyde used in the binder system is added as an aqueous formaldehyde solution of suitable concentration, e.g. commercial 37 # or Uit #.

When polyisocyanate and formaldehyde are used in the production of the raw material, their ratio is not critical. Usually, the optimum ratio for a given use can be determined by routine experimentation. A polyisocyanate-formaldehyde ratio of 2: 3 to 5: 1 has been successfully used. A ratio of about 1: 1 to U: 1 is usually used, for example, to control smoke problems or for economic reasons. Likewise, the amount of binder required for a given use can usually be determined by a simple experiment. With good results, 2-5% by weight of the # cellulosic material has been used. For the purposes of this weight, percentages and ratios, these are solid components unless otherwise indicated.

The cellulosic material from which the raw material for the inner layer of the coated product of the present invention is made consists of cellulosic material particles, usually wood particles, obtained from sawmill wastes, e.g. planing chips and Tenerih. Thus, the raw material is made from wood particle blends with up to about 30 # bark. Other ingredients include finely ground corn stalks, straw and paper strips. When chipboard-type products are made and formaldehyde and polyisocyanate are used as the binder system, the moisture content of the particles can be up to about 22% by weight. Usually, particles made from sawdust waste materials contain about 10-20% moisture and can be used without pre-drying. To achieve maximum economy of the drying step, particles with a moisture content in excess of about 6 # can usually be used. More moisture-containing particles can be used, but this will inevitably increase the cost of drying.

The raw material can also be prepared using an organic polyisocyanate of the type described above and without formaldehyde as a binder.

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The binder used in the preparation of the raw material from finely divided cellulose ** material can be sprayed onto the particles, which are rotated or mixed in a mixer. When the binder consists of polyisocyanate and formaldehyde, these can be added separately or together, the order of addition being irrelevant. When other materials are used in the raw material, e.g. wax, finishing agent or flame retardant, these are mixed into the finely divided material together with a binder.

In the manufacture of a coated product according to the present invention, e.g. plywood or paper coated particle board, the coating is made to contain phenol formaldehyde resin and form a coating on a porous base or padded raw material which finally forms the inner layer of the coated product. In the compression step, the phenol formaldehyde resin hardens and forms a weatherproof bond with the polyisocyanate-bonded cellulosic material of the inner layer. In addition, it has been found that the resin forms a barrier layer which prevents the penetration of the organic polyisocyanate through the coating. Thus, when using a resin in the manufacture of a reinforced product, coatings, e.g., thin plywood sheets and even paper, can be used without significant isocyanate-induced adhesion to the press film sheets. In addition, an excellent bond is formed between the cover and the inner layer of the reinforcing product. At least in part, this is thought to be due to a chemical reaction between the isocyanate binder and the phenol formaldehyde resin.

Usually, the amount of resin that binds to the inner layer of the coating is 11 to 86 g / m (based on solids).

When combined with a cellulosic material with an organic polyisocyanate binder, it is assumed that a chemical bond is formed with the cellulosic particles. In this case, the isocyanate groups of the polyisocyanate react with the free hydroxyl groups of the cellulosic materials to form urethane bridges. This reaction can be illustrated by the following scheme in which and are adjacent cellulosic material particles and R is an organic group representing the non-isocyanate portion of the polyisocyanate molecule.

63542 c7 "I — OH + 0 ~ ON- | ~ R | —N-OO + HO -j C2 _ 0 - 0, ----- [C1 RJ — NH-C-O — I C9

In addition, a portion of the polyisocyanate reacts with water in the raw material in the form of moisture to form a polyurea according to the scheme below, where R 1 and R 8 are organic groups representing the non-isocyanate moieties of different polyisocyanate molecules. When formaldehyde is present, the polyurea thus formed can react with formaldehyde to form a polyurea formaldehyde resin which promotes the association of cellulose particles.

- Rx -N-OO + H 2 O + Q «ON- | R2 - “P-. 9 r --— '--- Rx | —NH-C-NH— | R 2 | -H- CO 2 The phenol-formaldehyde resin of the coating which attaches the coating to the inner layer of the reinforcing product has phenolic hydroxyl groups capable of reacting with the isocyanate groups of the polyisocyanate to form urethane bonds generally according to the first scheme above. Thus, it is assumed that the coating resin forms a conventional adhesive-type bond with the inner layer as well as a chemical-type bond in the reaction described above, and further has the important function of forming a barrier layer preventing polyisocyanate from penetrating the coating and the film-forming film.

The invention is particularly useful in the manufacture of a coated article in which the coating is a sheet of paper attached to an inner layer. Paper is a relatively permeable material and usually the manufacture of a product using an isocyanate system as a binder for raw materials causes many problems when the coating is a sheet of paper. Addition of phenol formaldehyde to the coating gives very good products without the normally expected adhesion. A further advantage of the product is that when isocyanate is used as a binder for the cellulosic material of the inner layer, the formation of water vapor in the inner layer during the compression step is low, which reduces the blistering problems associated with the use of the coating. The rebound of the polyisocyanate-bonded inner layer is small, the expansion of the inner layer rings after the compression is completed. When the thickness of the inner layer is e.g. 1.59 cm, the rebound has usually been found to be less than 0.015 cm.

In the manufacture of a paper-coated product, it has been found that exceptionally good results are obtained when the coating paper is impregnated with water under pressure and heat before reinforcement. This is accomplished by spraying or spreading water on a roll of paper on the side of the paper sheet away from the porous base in the preparation of the raw materials prior to compression. The amount of water added is usually about 75-200 sheets of dry weight of the paper. By wetting the cover, during the compression step and because water vapor is formed in the region of the wetted sheet, the polymerization of the phenol formaldehyde resin apparently slows down until full pressure and close contact of the fine material of the inner layer is reached. Apparently, the moisture or steam generated is also able to plasticize the cellulosic material to some extent, which apparently improves the ability of the raw material polyisocyanate to bind the cellulosic material. Irrespective of the nature of the phenomenon, a product is formed which withstands the heaviest of the tests normally used to determine the outdoor suitability of reinforced products.

When applying the invention, the usual compression temperature is 135-220 ° C.

The following specific examples illustrate the invention.

Example 1

The paper-faced chipboard was prepared as follows:

A small green portion of Lodgepole pine with trunk, twigs, bark, and needles was fed into a chipper and ground in a hammer mill until it passed a 0.635 cm diamond sieve. From a batch of 2500 g of the fines formed, about 15 g of moisture was sprayed separately with 37 g of formaldehyde solution containing 23 g of formaldehyde and about 64 g of "PAPI" while stirring in a drum mixer. The raw material thus prepared contained about 18.2% by weight of moisture.

From such a raw material, a 6.35 cm thick porous base was made for a cover which was 0.046 cm thick "Crezon B210 sheet, manufactured by 8 63542

Crown Zellerbach Corporation. This is a sheet of paper treated with a phenol-formaldehyde resin and made by the cholesterol filling method, with a 0.0025 cm thick phenol-formaldehyde resin adhesive joint on one side (the weight of the adhesive joint is about 2 1 + 0.5 g / cm). The porous base was prepared so that the adhesive seam of the 'Crezon' sheet was facing up against the porous base. A second f, Crezon 'sheet was placed on top of the porous base and the resulting layer was compressed at a temperature of about 190 ° C and a pressure of about 22.1 kg. / cm for five minutes to a thickness of about 1.22 cm. The average density of the formed paper-coated chipboard was 697 kg / cm, the average modulus of fracture 137.37 kg / cm and the average modulus of elasticity 2 2l + 798 kg / cm when tested by ASTM methods.

Example 2

The freshly felled Lodgepole pine was finely ground as described in Example 1 and the raw material was prepared by mixing 1.5% by weight of PAP1 and 0.5% by weight of formaldehyde (added as a 37% formaldehyde solution) from the dry weight of the fine wood. calculated.

Particleboard coatings were prepared by spraying phenolic formaldehyde resin (1 + 8 # solid liquid resin, marked "0PA-197A" on the surfaces of 0.25 * + cm thick western larch plywood veneer, sold by 2

Coos Bay Division of Georgia-Pacific Corporation) at 21.5 g / m solids. An assembly consisting of a porous base obtained from Lodgepole pine and a plywood veneer attached to both sides was prepared. The adhesive seams of said coatings were inwards towards the porous base. The assembly was compressed as in Example 1 into a finished chipboard with a thickness of 1.9 cm and an average density of about 6 kg / m 2. According to the ASTM test 2, the average breaking modulus of the chipboard was about 1 + 61 + kg / cm and the average modulus of elasticity was about 69,250 kg / cm.

Example 3

A plywood-coated particle board product was made from a raw material obtained from planed chips of Ponderosa pine. The raw material was prepared by grinding in a hammer mill a 2 kg batch of chips until it passed through a 0.635 cm diamond sieve and added to the mixer. The moisture was 11.6 wt. In the mixer, the chips were sprayed with a 37 # aqueous formaldehyde solution with the addition of 1 + 7.8 g of formaldehyde and about 53.1 g of PAPIra1. To reduce the moisture uptake of the finished product, a microcrystalline wax emulsion with 50 wt% solid wax was also added. A suitable emulsion according to this description is "Paracol 915N", Hercules, Inc.

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The prepared raw material was formed into a porous base about 7.6 cm thick with a 0.25 cm thick Douglas spruce plywood spray-coated with 21.5 g / m 2 of phenol-formaldehyde resin ("0PL-19T ^") calculated as solids, thus forming an adhesive joint in the coating. A similar Douglas plywood veneer was spray-coated with resin and an adhesive joint was placed on top of the porous base, and the composition thus prepared was pressed at a temperature of 19 ± C and a maximum pressure of 22.1 kg kg / cin for about five minutes to a thickness of 1.27 cm. The 2 2 modulus was 773 kg / cm and the average modulus of elasticity 91 1 + 00 kg / cm.

Example 1+

In another preparation, 2.2 kg of Ponderosa pine planers, moisture 10 wt.%, Were placed in a mixer in which the chips were mixed with 99 g of liquid, approximately trifunctional polymethylene polyphenol isocyanate and 39-6 g of "Paracol 915N" raw material.

The coatings were made of 0.25 * + cm thick hardwood plywood veneers by applying 5 * + g / cm of solid resin to their surfaces. The resin used was phenol-formaldehyde resin, manufactured by Bordens ("MH-193-32", viscosity 300-50 cP at 25 ° C, pH 10.3 density 1.22 at 21 ° C) containing 1 + 0% solids.

A porous base about 6.35 cm thick was made from the raw material, which was placed on the resin-sprayed surface of the coating. It was pre-pressed in a cold press at a pressure of 0.01 + 9 kg / cm and the second cover was placed on the pre-pressed porous base with the resin surface downwards. The assembly thus formed was placed in a hot press and pressed for five minutes at 177 ° C. The maximum pressure was 21.1 kg / cm and the press was closed to obtain the desired thickness.

A 1.25 cm thick chipboard with an average density of 6 UU kg / m 2, an average breaking modulus of 7 ^ 9 kg / cm and an average elastic modulus of 85 63 * + kg / 2 cm was obtained.

Example 5

In a further preparation, a coated chipboard was prepared from the raw material according to Example H. The cover was made by placing a "Plyocite" sheet (a high density sheet of phenol-formaldehyde resin treated paper corresponding to 3.6.8. "High Density Overlay", U.S.Product Standard PS-I-7I + for

Construction and Industrial Playvood, Reichhold Chemicals, Inc., thickness 2 0.203 mm, weight 18l g / cm and resin solids content 50%) for film board, 0.25l + cm thick larch plywood veneer for high density sheet and "Plyophen" sheet for plywood veneer. "Plyophen" is a paper adhesive jointing product, 10__ 63542 with a continuous dry film of phenol-formaldehyde resin on a cellulose support, 2 manufactured by Reichhold Chemicals, Inc., thickness 0.069 mm, weight 67.14 kg./m and resin solids content 65 For a coating thus prepared, 4 cm porous base. It and the underlying coating were pre-pressed at a pressure of 0.049 kg / cm. A similar coating was then placed on the pre-compressed assembly with a paper adhesive seam against the porous base. The second film sheet was placed on the top cover and the whole assembly was placed in a hot press and pressed for five minutes at a temperature of 177 ° C and a maximum pressure of 22.5 kg / cm 2. A chipboard of thickness was obtained

Ύ O

1.217 cm, density 663 kg / m 2, breaking modulus 1332 kg / cm 2 and elastic modulus 161,340 kg / cm 2.

As described above, the invention makes it possible to produce an excellent coated product, the coating of which consists of a water-permeable material, e.g. paper, which is impregnated with water before the use of heat and paste. The following example illustrates this type of manufacturing.

Example 6

A coated particle board product was prepared using the raw material of Example 4. On the other side of the sulphate cellulose sheet (127 g / m 2), a phenol-formaldehyde resin adhesive joint was prepared by spraying it with the phenol-formaldehyde resin of Example 4 in an amount of 53.9 g / m 2 of resin (dry matter). Water was sprayed on the opposite side of the sheet, which was retained on the sheet of paper at about 172 g / cm 3. A moistened sheet of paper was placed on the film sheet with the resin coated side up.

A porous base about 3.81 cm thick was prepared for this sheet and it and the underlying coating were pre-pressed at a pressure of 0.049 kg / cm. A second coating was prepared, which was placed on the precompressed assembly with the coated side of the moistened sheet facing the porous base. The second film sheet was then placed on the top cover and the whole assembly was placed in a press and pressed for three minutes at a temperature of 177 ° C and a maximum pressure of 21.1 kg / cm 2.

A chipboard with a thickness of 0.734 cm, a density of 717 kg / m 2, a refractive index of 224 kg / cm 2 and a modulus of elasticity of 31,970 kg / cm were obtained. After four hours of cooking, the sample did not delaminate.

Example 7

The chipboard described above can be further processed to obtain a plywood coated product. Thus, 0.254 cm thick hardwood veneers sprayed with the resin of Example 4 were prepared and the adhesive joints were air dried for two hours. Liquid polymethylene polyphenyl isocyanate was applied to both sides of the paper-coated product in an amount of 43 x 06 g / m 2. The paper-coated, isocyanate-coated product was placed between the larch veneer resin surfaces per paper-coated chipboard. The assembly was then placed between the membrane plates and pressed for three minutes at a temperature of 177 ° C and a maximum pressure of 12.5 kg / cm 3. A very good plywood-coated particle board product was obtained which did not delaminate when cooked for four hours. The chipboard had a thickness of 1.217 cm, a density of 687 kg / m 2, a modulus of fracture p 1010 kg / cin and a modulus of elasticity 116 862 kg / cm.

In the above examples, no polyisocyanate-induced adhesion to the film sheets could be observed. Thus, there was no need to use a release agent to prevent such isocyanate-induced adhesion.