RU2252867C1 - Method for manufacture of splint-slab plates - Google Patents

Abstract

FIELD: production of building materials, applicable in the wood-working, furniture and building industries.

SUBSTANCE: the method consists in mixing together of wood particles with urea-formaldehyde resin, butadienstyrene methacrylic latex, ammonium chloride and Aerosil, forming of the mat, cold prepressing and hot pressing. The binder instead of ammonium chloride contains ammonium fluosilicate at the following relation of the components, mass percentage: urea-formaldehyde resin - 82.8 to 93.4, ammonium fluosilicate - 0.6 to 1.2, butadienstyrene methacrylic latex - 4.0 to 12.0, Aerosil - 2.0 to 4.0.

EFFECT: enhanced physico-mechanical and ecological characteristics.

2 tbl

Description

The invention relates to the production of building materials and can be used in the woodworking, furniture and construction industries.

A known method of manufacturing a particle board based on modified urea-formaldehyde resins with latex compositions, comprising treating the particles with a composite binder followed by hot pressing (I.Iosifov et al. Properties of particle boards based on urea-formaldehyde resins modified with latex compositions, Higher Forestry Institute, Sofia, IX Symposium 9, 1989, pp. 185-189).

The disadvantages of this method are the use of styrene-butadiene latexes that do not contain carboxyl groups, thickening additives in the form of latex with a high content of methacrylic groups, as well as the absence of an active filler capable of effectively adsorbing residual formaldehyde. Emission from finished plates of this compound, which has carcinogenic and mutagenic properties, makes the use of plates in construction extremely difficult and virtually eliminates their use in the furniture industry.

A known method of manufacturing chipboards from woodworking industry waste, including mixing wood particles with a binder containing urea-formaldehyde resin, ammonium chloride, a mixture of styrene butadiene carboxylate and methacrylate latexes, OP-10 emulsifier, trisodium phosphate and aerosil, forming carpet, cold forming, carpet forming pressing (RF patent No. 2074090, class B 27 N 3/04, 02.27.1997).

The disadvantages of this method are the low strength and water resistance of the plates, as well as technological difficulties associated with the complex composition of the composite binder.

The closest in its technical parameters is the method of manufacturing chipboard (RF patent No. 2176186, class B 27 N 3/02, C 08 L 97/02 // (C 08 L 97/2, 61:24) 11/27/2001, Bull No. 33), including the mixing of wood particles with urea-formaldehyde resin, styrene butadiene methacrylate latex, ammonium chloride and aerosil, carpet formation, cold pressing and hot pressing, the binder contains these components in the following ratio, wt.%:

urea-formaldehyde resin - 76.4-93.2

ammonium chloride - 0.8-1.6

styrene butadiene methacrylate latex - 4.0-12.0

Aerosil - 2.0-10.0

A significant drawback of this hardener is the following: during the hydrolysis of ammonium chloride, ammonium hydroxide and hydrogen chloride are formed, which is currently recognized as carcinogenic to humans. Ammonium hydroxide and hydrogen chloride formed during hydrolysis under conditions of high-temperature (140-170 ° С) curing pass into the vapor-gas phase in the form of ammonia and hydrogen chloride, the concentration of which decreases as a result of removal together with the vapor-gas medium through the edges of the pressed plate material. The latter circumstance adversely affects the uniformity of the cured resin and thereby reduces the strength properties of the final slab material.

The objective of the invention is to increase the physico-mechanical properties of plates, as well as improving the environmental properties of plate materials, which expands the scope of their application.

To solve this problem, in a method for the manufacture of chipboard, including mixing wood particles with a binder containing urea-formaldehyde resin, aerosil and styrene-butadiene methacrylate latex containing in the copolymer units, wt.%: Butadiene - 25, styrene - 20, carpet formation and hot pressing, binder contains ammonium silicofluoride as a hardener in the following ratio of components, wt.%:

urea-formaldehyde resin - 82.8-93.4

ammonium silicofluoride - 0.6-1.2

styrene butadiene methacrylate latex (BSMK) - 4.0-12.0

Aerosil - 2.0-4.0

The effect obtained from the use of ammonium silicofluoride as a hardener can be explained as follows. Ammonium silicofluoride [(NH ₄ ) ₂ SiF ₆ ] is an ammonium salt of silicofluoric acid, which is readily soluble in water and, like ammonium chloride, undergoes hydrolysis to form an acidic medium necessary for the cure of the urea-formaldehyde resin. Moreover, the hardener proposed in this composition has a complex effect. Silicon fluoric acid, approaching sulfuric in strength, is capable of producing acidic medium necessary for curing the resin at lower hardener concentrations, and also, having insecticidal properties, provides them with plate materials, which acquire a wider range of applications. Ammonium cation is contained in this compound twice as much as ammonium chloride, which is the hardener for the resin in the prototype. This feature of ammonium silicofluoride is an advantage, since hydrolysis produces a larger amount of a weak base - ammonium hydroxide, which easily decomposes with the formation of ammonia, which is an active acceptor of free formaldehyde and increases the environmental performance of plate materials and expands their field of application.

In this case, BSMK latex, which does not require additional thickening and stabilization, has a minimum colloidal particle (micelle) size and is easily distributed in a urea-formaldehyde resin. Under conditions that are characteristic of hot pressing, i.e. at elevated temperatures up to 165 ° C and the presence of an acidic catalyst (ammonium silicofluoride), a more intense interaction of the carboxyl groups of the latex with the methylamine or oxymethyl functional groups of the resin with the formation of a three-dimensional integral structure of the adhesive joint. The introduction of BSMK into the resin in a certain interval allows you to adjust the frequency of "crosslinking" (or M _{with the} molecular weight of the chain between the nodes in the three-dimensional polymer) between the macromolecules of the resin. Thus, BSMK latex, acting as an auxiliary "cross-linking" agent for the resin, provides the formation of a more regular, ordered structure of the cured resin, which is characterized by a smaller number of structural defects of the grid. The latter circumstance contributes to the growth of cohesive strength of the adhesive joint and the strength characteristics of the plate.

In this case, along with cohesive strength, high adhesion of the binder to the surface of wood particles is ensured. An active filler, Aerosil (TU 14-922-77), which is a specially manufactured finely divided silica with a developed hydroxylated surface, plays a significant role in this. Filling micropores of wood particles, Aerosil thereby increases the useful area for gluing wood particles together. Being a polar oxygen-containing substance, Aerosil provides a high degree of saturation with hydrogen bonds between wood and polar groups of the composite binder. The physicochemical properties of Aerosil have a significant effect on the content of free formaldehyde. Probably, Aerosil, along with latex, is actively involved in the curing of the resin, preventing the formation of vapor-gas bubbles, where residual formaldehyde is concentrated, and ensures the chemisorption of the latter due to the presence of contact micropores and uneven chemical bonds of the hydroxylated surface of the aerosil particles. However, the use of ammonium silicofluoride as a hardener makes it possible to reduce the aerosil content due to the noted increased ability of ammonium silicofluoride to bind free formaldehyde. An important circumstance is that the chemisorption of formaldehyde by aerosil is carried out at a temperature below the pressing temperature of the particle board. Therefore, under conditions of high-temperature pressing, Aerosil does not significantly affect the rate of polycondensation processes and thereby does not decrease the productivity of the process.

Reducing the emission of residual formaldehyde is also achieved due to the ability of formaldehyde to join in an acidic environment through the double bond of methacrylate latex.

The method is as follows.

Chip-sawdust is dried in a convective type laboratory drying chamber to a moisture content of 2-4%. A binder is prepared by mixing a urea-formaldehyde resin with a latex composition, aerosil and ammonium silicofluoride.

The concentration of the binder in this case is 57-67 wt.%, The conditional viscosity in B3-4-150-170 sec. The binder consumption of 12% by dry solids to the mass of absolutely dry wood particles. The ratio of chips to sawdust by weight is 65:35.

Wood particles are mixed with a composite binder using a pneumatic atomizer in a laboratory mixer. The carpet is formed from glued wood pulp using a wooden frame, pressed in a cold press and pressed in a hot press at a plate temperature of 150 ° C, a pressure of 2.5-3.0 MPa and a duration of 0.5 min / mm. Single-layer plates with a thickness of 12 mm are made. After pressing, each plate is cooled in an upright position without blowing at room temperature. The plates were tested no earlier than 5 days after manufacture.

In accordance with the above technology, plates were obtained according to the prototype (example 1) and the proposed method, changing the composition of the binder (examples 2-6 of table 1).

Table 1 Components The content of components, wt.% According to the example 1 2 3 4 5 6 (prototype) Urea-formaldehyde resin 86.8 96.6 93,4 87.2 82.8 77.6 Ammonium chloride 1,2 - - - - - Ammonium silicofluoride - 0.4 0.6 0.8 1,2 1.4 Styrene butadiene methacrylate latex 8.0 2.0 4.0 8.0 12.0 16,0 (BSMK) Aerosil 4.0 1,0 2.0 3.0 4.0 5,0

Plates with different binder composition, made according to the above technology, were tested for physical and mechanical properties and free formaldehyde content. The performance of the tested boards are shown in table 2.

table 2 Indicators Examples 1 2 3 4 5 6 (prototype) Bending Strength, MPa 23.9 19.9 24.7 26.9 25.8 20.1 Tensile strength perpendicular to the reservoir, MPa 0.78 0.76 0.81 0.85 0.82 0.77 Thickness swelling,% In 2 hours 10.7 14.3 9.5 8.7 9.2 18,4 In 24 hours 16.3 23,2 14.7 13.3 15.1 22.5 Density, kg / m ³ 731 740 742 731 750 745 The content of free formaldehyde, mg / 100 g plate 9.2 11.7 8.8 7.2 8.5 10.3

As follows from the data in table 2, the plates obtained by the proposed method have higher strength and water resistance, and the emission of free formaldehyde is lower than in the prototype.

Claims (1)

A method of manufacturing chipboards from wood processing industry waste, comprising mixing wood particles with a binder containing a urea-formaldehyde resin, styrene butadiene-methacrylate latex BSMK with a content in the copolymer of units, wt.%: Butadiene 25, styrene 20, methyl 35 methacrylate, 20 methacrylate and aerosil, carpet formation, cold pressing and hot pressing, characterized in that the binder as a hardener contains ammonium silicofluoride in the following ratio onentov, wt.%: urea-formaldehyde resin 82.8-93.4 ammonium silicofluoride 0.6-1.2 styrene butadiene methacrylate latex (BSMK) 4.0-12.0 Aerosil 2.0-4.0