DE2716375A1 - Wood particle boards - made using aminoplast adhesive with peracid hardener - Google Patents

Abstract

Hot pressed particle boards etc. are made from particulate cellulose-contg. materials and an acid cured aminoplast binder. The hardener used for the adhesive is a peracid and/or a precursor of this, opt. mixed with other adjuvants. The use of peracids such as peroxydisulphuric acid, ammonium persulphate, etc., as hardener for the amino resin gives rapid cure of the binder at lower temps. (60-90 degrees C) than those normally used in the prodn. and overcomes problems associated with the formation of steam in the interior of panels, etc., when using the higher temps. used previously.

Description

"Shaped wooden body"

The invention relates to molded wooden bodies based on cellulose Particles made by aminoplast glues hardened with acidic hardeners and optionally further additions are connected to each other.

Wood-based molded bodies made of aminoplast-glued, small-scale cellulosic material by pressing in the heat in the presence of acidic Hardeners are made have long been known. As a small-sized cellulosic one Material can be a wide variety of substances, mainly of vegetable origin from dusty material to fibrous material to insulating shavings and coarse wooden sticks be used. Lignified particles, such as wood fibers, are particularly preferred Chip material. In this case, the molded lignite material can be made from mixtures of Particles of different sizes, for example that of the wood chip moldings, as in the manufacture of chipboard, fine material as well as wood chips of various sizes exist, albeit the layered arrangement of the lignified ones Particles according to the respective order of magnitude, is often preferred. Shaped wooden body Particle boards, for example, are of particular interest, mostly as multilayer boards are formed and in which layers of different chip size and chip thickness are provided and which often have a top layer on their surfaces, the fine material, in particular the chipboard sanding dust produced during thickness sanding, contain.

Aminoplast gluing leads to the manufacture of molded wood-based bodies with acid hardeners under heat and pressure to products of considerable strength. A Another advantage is that the aminoplast glues are easy to process. The aminoplast glues are alkaline and are made using acidic compounds, i. after creating an acidic environment, preferably under heat and Pressure, hardened. Since the hardening process after the addition of the acidic compound is relatively starts quickly, the glue is applied before or after it is applied to the the particles to be glued are provided with a curing system that only for example when heated. This can mainly be done in that a mixture is used as hardener, which is initially added by adding alkaline substances is brought to an alkaline range. By volatilizing aer alkaline as Buffer-acting substances, initially physically or chemically masked with release acidic substances, e.g. when the effect of heat, is then the pH value of the glue moved to the acidic range for hardening.

A common bracer consists, for example, of a mixture of ammonium chloride, ammonia and water; the ammonia is volatilized when heated and the ammonium chloride and the hydrochloric acid, which has been set free, effect this Hardening in the acidic medium thus obtained. Since hardening using Hardening of the aforementioned type only starts in a technically usable manner at around 900 C, The resin particles must have sufficient strength to make resin articles heated to at least this temperature and sufficient time at this temperature being held; in practice, the temperature rises to around 1100 C and more. the Gluing time determines the processing speed. It misaligned afterwards the efforts to reduce the gluing or heating time as much as possible keep it short.

For a satisfactory hardening according to quality and time a certain one is required Amount of acidic hardener necessary. A larger amount of acidic hardener shortens the heating time does not, but it embrittles the glue and is not used up during hardening, that is, residual amounts of acid remain active and have an adverse effect in general the properties of the wood material moldings and especially their mechanical ones Strengths.

The object of the invention is accordingly to produce molded wood-based bodies to provide the basis of small, cellulosic material, wherein the particles by means of aminoplast glue hardened with acidic hardeners and optionally further additives are connected to one another, and the molded body despite being shortened Heating time fully satisfactory properties, especially mechanical strength properties exhibit.

The object is achieved in that, in the case of molded wooden bodies of the aforementioned type as hardener peracids and / or their precursors or mixtures, which contain peracids and / or precursors are used.

Aminoplast glues primarily include the well-known angry hardening formaldehyde condensation products, especially with urea and melamine Understood. The glues can contain customary additives, such as fillers and extenders, for example Wood flour, mineral powder, but also other known adhesives or the strength properties Contain supportive compounds such as starch and protein flours.

Peracids in the context of the invention are primarily the (inorganic) Peroxy acids, as well as the (organic) peroxy acids. Decisive is the presence of the -O-O-group, which has an oxidizing effect under the conditions of use, in addition to an acid group. The oxidizing ability of the peracids can be for example in the oxidation of formaldehyde to formic acid at elevated temperatures recognize in the glue.

Inorganic peracids, such as, for example, are particularly suitable Peroxoboric acid, peroxomono- and disulfuric acid, peroxomono- and diphosphoric acid, Peroxo nitric acid, but also acids of the perchloric acid type.

The lower aliphatic in particular come as organic peracids Peroxy acids, such as performic acid, peracetic acid, but also peroxyarylcarboxylic acids with one or two, optionally condensed, aromatic rings, such as, for example Perbenzoic acid. However, peracids in the context of the invention also include the so-called To understand diacyl peroxides, such as, for example Di-tert-butyl peroxide or benzoyl peroxide.

Precursors within the meaning of the invention are substances or mixtures of substances, which contain the peracids in a physical or chemical form, so that, in a mixture with aminoplasts, hardening of the aminoplasts only under gluing conditions, especially in the warmth. Only then are the peracids under displacement the pH value in the direction of acidic areas and development of the oxidative effect set in freedom. In particular, the peracids can be mixed together with Gluing temperature volatile bases such as ammonia or amines are present, with the bases usually exceed the stoichiometric amount required for salt formation will. Preferred precursors of the peracids are their ammonium salts, such as, for example Ammonium peroxo-monosulphate or disulphate, ammonium peroxo-noiophosphate or diphosphate, Ammonium peroxonitrate, ammonium peroxyformate, the ammonium salt of peroxybenzoic acid as well as others that release peroxyacids only under gluing conditions Peracid derivatives. Precursors in the context of the invention are also microencapsulated Peracids or peracid derivatives with only degradable under gluing conditions Capsule material. In the molded articles according to the invention as Hardener exclusively the peracids or their precursors as well as mixtures of Per acids or precursors with other substances, including previously known hardener or hardener constituents may be used.

Such molded wood-based bodies according to the invention have particular advantages on, their gluing in the presence of an additional amount of formaldehyde, besides the aldehyde which is already present in the aminoplast.

Instead of formaldehyde, other lower aliphatic aldehydes can also be used be used, preferably in amounts of 1 - 7% by weight, in particular about 3% by weight, based on the 65% aminoplast glue.

The wood-based material molded bodies according to the invention have, despite essential shorter heating times at least the same good general and mechanical properties Strengths like the well-known wood-based molded bodies made with aminoplast adhesives can be produced using the previously known hardeners.

A particular advantage of the molded objects according to the invention is also that the mechanical strength achieved in a short heating time also did not have to be bought with higher temperatures. Temperature increases Find soon their limit due to the water contained in the wood, which evaporates at 1000 C. The steam leads to incorrect gluing, steam bubbles and bursting. Wood-based molded bodies are produced poor ligament and strength. at the high temperatures that occur at the previous hardener systems are necessary to achieve portable heating times, the correct water balance is a problem of the first order.

The wood material Fonakurper according to the invention are thanks to their adjustable in the hardness range of 60 - 900 C inside the molded body instead of the previously necessary Temperatures of about 30 - 1100 C and more from all due to the development of steam Errors and the resulting mechanical defects free.

As the tests have shown, the wood material molded bodies according to the invention have with a heating time shortened by approx previously produced moldings with a heating time of about twice as long. It is to note that the wooden objects according to the invention, thanks to the fact that they at low heating temperatures can be produced, from all those defects, in particular Glues of low strength (incorrect glues) are free, which are known in the case of known Wooden objects, the gluing of which is inevitably carried out at elevated temperatures had to occur inevitably. In addition the license period is shortened and synonymous with gentler material handling.

Examples of the molded wood-based bodies according to the invention are here mainly chipboard or others made using wood chips Moldings, wood fiber boards, doors made from such boards and moldings, Elements for floor, wall and corner cladding and the like.

Within the scope of the invention, there is the method for producing Shaped wood-based bodies with pressing in the heat of Aminoplant glues and optionally further additives glued, small-sized, cellulose-containing Material, in the presence of acidic hardeners, in that as harder peracids and / or their precursors or such entialtenuated mixtures were used. Are preferred here precursors, in particular peroxodisulfuric acid and / or its ammonium salt or mixtures containing them. The components of the mixture include, for example, basic, Substances that can be volatilized under gluing conditions, such as ammonia and urea, liexamethylenetetramine, volatilizable carriers, water or others known per se Harder to consider.

According to a further preferred embodiment, the method in the presence of an aldehyde additive exceeding the aldehyde content of the aminoplast glue, preferably in amounts of 1 - 7% by weight, based on the 65% strength isminoplast glue. In particular, formaldehyde or lower aliphatic aldehydes are used. The process can have a hardness range of about 60 - 900 C, with the steel plate temperatures of the press between can have about 100 to 2000 C, in particular 100 to 1400 C. They are the usual ones Urucke can be used up to approx.

Gel time is generally used as a measure of cure rates is used by glues, according to the invention, for example, 1 min., 33 Sec must be reduced to 51 Sec. This corresponds to a reduction of 45%.

The mode of operation of the peracids used according to the invention is not adequately clarified. The peroxo group may create formaldehyde oxidized to formic acid, a reaction that starts relatively early and thus the production of molded wood-based bodies with standardized mechanical strengths with shortened heating times.

The example below shows a molded wood-based body according to the invention with a wooden object manufactured according to known processes, with otherwise the same Conditions, compared EXAMPLE 1 Chipboard is a wood-based material from chips of various sizes, usually by means of aminoplast glueing together are glued. They are usually built up in several layers, with the transition from the middle layers of coarser chips to the outer layers of finer chips is more or less sharply delimited depending on the manufacturing process. For binding of the glue, the molded wood-based body must reach the necessary hardening temperature be completely warmed through.

In the case of a conventional glue-hardener mixture, for example the glue is made from a proprietary urea resin and the hardener is made from a mixture of 20 Parts by weight of ammonium chloride, 5 parts by weight of ammonia and 75 parts by weight Water. 10 parts by weight of this hardener mixture are added to the urea resin. The gel time is about 93 seconds at 98 ° C.

With such a prepared glue-hardener mixture, the chips glued, shaped into a loosely piled chip cake in a molding machine and in a multi-daylight or single-daylight press under pressure and heat for the wood-based panel pressed with simultaneous hardening of the Glue. The pressing time is largely determined by the curing temperature, the curing time and the penetration time the warmth. The heat is conveyed through the heatable steel plates of the press transferred to the compact and passed into the interior. The soaking time is mainly determined by the temperature of the steel plates and the thickness of the chipboard.

The latter had an average thickness of 20 mm.

With the glue-hardener mixture described above, an optimal Pressing time at a curing temperature inside the pressed part of around 90 - 1100 C reached.

If the steel plate temperature is around 130 to 1400 C, the pressing time is about 6 minutes.

A hardener mixture is used to produce the chipboard according to the invention from 20 parts by weight of ammonium persulfate, parts by weight of 25% ammonia and 7 parts by weight Water produced. From this mixture again 10 parts by weight per 100 Parts by weight of 6)% strength urea resin are added. The gel time is at 980 ° C about 51 sec. Under the same pressing conditions as before, the compact only consumes To be heated 60 to 900 C and the pressing time is then only about 3.5 minutes. That means a shortening of around 40 t.

With this shortening, it should be noted that it is not only limited by the Shortening of the Geliereit arises, but above all because of the fact that the Durcllwärmung the faster it happens, the greater the difference in temperature. At a Steel plate temperature of e.g. 1400 C, the pressed part is heated inside to 60 ° C comparatively much faster than to 900 C. The harder according to the invention However, it is already effective at 600 C. Until then the temperature inside rises 900 C has risen, the hardening has already ended, where it was with the conventional one Hardener only begins to take effect.

A further shortening of the heating time is for the production of the invention Moldings possible by adding formaldehyde without increasing the temperature. True was earlier attempts were made to shorten the heating time by increasing the temperature. at One-daylight presses went up to about 2200 C in aen steel plates. But that is very dangerous because the temperature in the outer zones of the compact is high rises above 1000 C, the evaporated water from the penetrating heat into the interior the board is driven and then glue damage to the point of explosion Burst of the whole plate can be triggered.

The moldings of the invention are maintained more economical lease periods and with far better possibilities for variation in the entire manufacturing process, e.g. in the coordination between pre-drying of the chips and steel plates - temperature manufacturable. This has a considerable influence on properties and production costs the molded body. Also a variation of the hardener between the outer and inner ones onening the chipboard or moldings is possible. Moldings can be produced in this way, in the case of those, as opposed to an all too rapid hardening of the outer rapidly heated zones To avoid the inner ones, hardeners for the glue are used in the outer ones Harden zones more slowly and faster in the inner areas. This can be done, for example, by Reached different proportions of the components of the iiärtergemisches in kind and rod will. One possibility is to change the peracid or Peracid precursor content, e.g. the ammonium monopersulphate content of about 0.5% by weight, based on 65% aminoplast glue in the top layer to 1.3% by weight in the middle layer. Another, possibly additional, option is to use Urea, formaldehyde, hexamethylenetetramine and the like. But also other measures such as changing the pressing diagram, pressing temperature and comparing for Variations of the hardening effect can be used.

Claims (4)

Claims: 1. Shaped wood material based on cellulose Particles made by aminoplast glues hardened with acidic hardeners and optionally further additions are connected with each other, d u r c h e k e n n z e i c Not that the hardener per acids and / or their precursors or containing them Mixtures are used. 2. Shaped wooden body according to claim 1, d a d u r c h it is not noted that inorganic per acids and / or their as hardeners Precursors, in particular peroxodisulfuric acid and / or its ammonium salt or mixtures containing such are used. 3. Wood-based molded body according to claim 1 or 2, d a d u r c h g e k e n n n z e i c h n e t that as further additives formaldehyde, preferably Are used in amounts of 1 to 7% by weight, based on the aminoplast glue. 4. Shaped wooden body according to one of the claims 1 to 3, d a u r c h g e k e n n -z e i c h n e t that Ilärter is used in the outer layers that act more slowly than the hardeners at lower temperatures at the same curing temperatures Layers.