RU2708582C1 - Filling paste for covering veneer defects and method of producing plywood using filling paste - Google Patents

Abstract

FIELD: woodworking industry.

SUBSTANCE: invention relates to woodworking industry and can be used in production of glued laminated materials, particularly veneer. Filling paste for covering veneer defects contains phenol-formaldehyde resin, chalk, flour, water, wherein the paste additionally contains kaolin and mimosa extract, with the following ratio of components, wt%: phenol-formaldehyde liquid resin 70.0–75.0, wheat flour 6.0–10.0, chalk 4.0–6.0, kaolin 10.0–12.0, mimosa extract 1.0–2.0, water balance. Method of producing plywood includes gluing sheets of veneer by hot pressing and covering defects of plywood with filling paste, note here that plywood defect cover is performed by said hot curing filling paste by layer-by-layer filling of veneer sheets defects immediately prior to hot pressing.

EFFECT: production of plywood with application of filling paste to eliminate almost all defects of veneer (wood) and creation of surface for subsequent lamination of the product.

2 cl, 3 tbl

Description

Filling paste for covering veneer defects and a method of manufacturing plywood using filling paste.

The invention relates to the woodworking industry and can be used in technological processes for the production of glued laminated materials, in particular plywood. The invention provides the possibility of producing plywood using filling paste to eliminate almost all defects and defects of veneer (wood) and create a surface for subsequent lamination of products.

As a prototype, a glue recipe for a spray application line was selected.
(based on Hexion Specialty Chemicals, USA) - information taken from https://lesprominform.ru/jarticles.html?id=4373. The specified recipe includes the following components, wt.%:

Phenol-formaldehyde resin (it is also phenol-formaldehyde) - 62.8

Wheat flour - 5.2

Corn flour - 4.4

Water (t = 30-42 ° C) - 20.2

Chalk - 3.6

Sodium carbonate (soda ash) - 1

Caustic soda (50% solution) - 2.8

Adhesive deficiencies are also indicated there: the difficulty in adjusting the adhesive flow rate and spray quality, as well as the greater sensitivity to adhesive viscosity and the presence of particles and clots in it. Cleaning and flushing the glue circulation system took a long time and required a large amount of water. At the subsequent start-up of the line, a certain amount of water inevitably remained in the system and mixed with the supplied glue, which led to marriage when the veneer packets that were first bonded after gluing were glued.

The objective of the invention was to improve the quality of the final product - plywood, and the corresponding technical result is to increase the yield of products that meet regulatory requirements.

This problem will be solved by filling paste to cover defects in veneers containing phenol-formaldehyde resin, chalk, flour, water, which, according to the proposal, additionally contains kaolin and mimosa extract or Querbaho extract, in the following ratio of components, mass. %:

Phenol formaldehyde resin - 70.0-75.0

Wheat flour - 6.0-10.0

Chalk - 4.0-6.0

Kaolin - 10.0-12.0

Mimosa extract - 1.0-2.0

Water is the rest.

This paste is a hot cured product.

The problem is also solved by the method of manufacturing plywood, including gluing veneer sheets by hot pressing and covering defects of plywood with filling paste (see also: https://lesprominform.ru/jarticles.html?id=4373), while covering the defects of plywood is done by the proposed paste hot curing, by layer-by-layer filling of defects in veneer sheets immediately before hot pressing. At the same time, the classical technology of plywood production is being modified. Several technological operations are added. Thanks to new technology, the production process leads to new quality indicators and economic benefits.

The filling paste in its properties is ideally suited for repairing, repairing peeled veneers of all types of wood and thereby removes all visible and hidden wood defects and sheet defects.

The following is a description of the process and the formation of defects. Peeled birch veneer.

The log after cylindering is peeled on a continuous veneer tape. Due to the high speed of peeling, the veneer tape obtained during cutting first arrives in the form of waves on the looper table (this allows a noticeable reduction in the length of the peeling line) and then is fed to scissors, where it is cut into sheets of a given format. Sheets are stacked on a conveyor in stacks and transported to a drying chamber, where the veneer is dried to a moisture content of 6–8%. After drying, the veneer sheets are fed to a longitudinal conveyor, where they are sorted by quality and stacked in format-sized stacks. The pressure of the peeling knife and counter knife (ruler) causes compression and bending in the cross section of the wood fiber. Since the tensile stresses from bending are usually larger in magnitude than the compressive ones at the blade, the prevailing tensile stresses act.

Due to the weak resistance of wood to stretching along the fibers as the cutter is introduced, tensile stresses first reach the tensile strength of the wood, which leads to the formation of cracks on the bottom surface of the veneer.

Cracks form with a certain step and do not extend to the surface of the chip, since compressive forces prevail there. As a result, a drain tape-like chip with cracks is formed on the inner side, which negatively affects the mechanical strength and appearance of the veneer.

Since the entire volume of churak is dissolved on the veneer, defects are formed on the surface of the obtained veneer, most often due to the loss of layers of cut knots, cracks due to drying, as well as other structural defects in the wood. Therefore, veneer packs after sorting are sent to remove such defects - veneer. Veneer repair is carried out to increase the grade by one category by cutting a knot in the form of an ellipse from a knot sheet and inserting a patch of the same shape into this hole. Patches with a moisture content of 3-5% of the same thickness as the veneer sheet are installed with a tightness of 0.1-0.2 mm. Depending on the size of the defects, four standard sizes of patches are used - from 25 × 15 to 100 × 60 mm. Patches (inserts) can be in veneer for a rather limited time. This is due to constant changes in humidity and, accordingly, a change in the gap between the veneer and the insert. As a rule, after two weeks of storage - inserts fall out.

The reduction in the quality of the veneer itself is also due to wood defects. Wood defects include:

- knots healthy, unhealthy, pin;

- zakorina;

- wormhole;

- cracks closed and dispersed;

- a dent, prick, cut;

- resin pocket;

- rot;

- rough peeling

The technology of using the inventive paste is self-sufficient for repair and repair of both veneer defects occurring during peeling, and all of the listed wood defects. The properties of the paste allow you to create a flat surface in the place of the defect / defect and give this area increased physical and mechanical properties that exceed the standard parameters of healthy wood.

The following discloses in detail the meaning of each component of the filling paste to achieve the claimed technical result.

Phenol-formaldehyde resin (for example, resin SFZh 3013 or SFZh 3014 (according to GOST 20907-75)). Homogeneous clear liquid from reddish brown to dark cherry color. The resin is a polycondensation product of phenol with formaldehyde in the presence of an alkaline catalyst. It is used as a binder for other components and a catalyst for the formation of a rigid polymer compound under the influence of temperature and pressure. The proportion in the composition of the paste is 70.0-75.0%, depending on the initial viscosity. Standard viscosity of 70 seconds on the viscometer No. 4. The standard temperature of the resin is 20 ° C. Below 14 and above 28 degrees can not be used.

Technical kaolin (according to GOST 19607-74). Kaolin is a mineral filler obtained by grinding and separating white clay, rock, which consists mainly of the kaolinite mineral. Features of kaolin: it has a moisture content of up to 1%, which makes it an indispensable material in the production of paste (the claimed paste has good hiding power, flowability and strength due to kaolin). This filler is characterized by a rather low density, easy dispersibility and a complete lack of abrasiveness. Also, kaolin helps increase the density of the paste. In the composition of the paste, the proportion of kaolin is 10.0-12.0%.

Additional requirements for kaolin: in addition to the fact that kaolin must be in strict accordance with GOST 19607–74, it is necessary to control the content of arsenic lead and mercury in it. These substances should not exceed the maximum permissible concentration (maximum permissible concentration) according to GOST 31676-2012.

Technical chalk (GOST 8253-79). The use of chalk in the production of filling paste as a filler can significantly reduce the cost of this product and improve its quality. Chalk is insoluble in water, has no abrasive properties. Almost no impurities.

The main purposes of chalk in the paste are three:

1. Chalk in suspension, in a liquid medium, helps to significantly dissolve or dilute other components. Due to the fact that it is first mixed with SFG resin, chalk makes a “porous medium” capable of easily dissolving or mixing other components.

1. Chalk, penetrating into the structure of defects, quickly clogs the porous places and thereby clogs the wood base and does not allow the liquid to penetrate beyond the intended place.

2. Chalk, being in the composition of the paste, at the time of initial curing prevents the metal plate of the hydraulic press and plywood from sticking together at the place of its completion with the paste. And after the initial hot cure, it helps to make the repair place suitable for subsequent grinding. The high dispersion of crushed calcium carbonate has a positive effect on the smoothness and porosity of the plastic sheet finalization site. The amount of chalk in the total mass of the paste is 4.0-6.0%.

Standards of technical chalk values are given in table 1.

Tab. one

The name of indicators Norm Calcium carbonate + magnesium carbonate,%, not less than 98.2 One and a half oxides (R2O3),%, no more 0.4 Insoluble residue in hydrochloric acid,%, not more than 1.3 Manganese,%, no more 0.15 Copper,%, no more 0.001 Iron oxide (Fe2O3),%, no more 0.15 Consolidated alkali in terms of CaO,%, no more 0.02 Water-soluble substances,%, no more 0.1 Ions SO''4 and Сl 'in an aqueous extract,%, no more 0.04 Iron extracted by magnet,% no more 0.02 Sand,%, no more 0.02 Humidity,%, no more 0.2 Reflection coefficient,%, not less 90.0 The residue on the sieve size: 0.2,%, not more than 0.14,%, not more than 0.045,%, not more 1,0

Wheat flour 1 grade. Flour is present as an active filler. Increases the total viscosity of the cooked mass for a period of 20-25 minutes to the desired state. If, for example, the resin with kaolin has a viscosity of 100 seconds (heavy cream), then with the help of flour, the viscosity can be increased to “thick sour cream” without a special increase in weight and density. This effect is especially necessary for the polymerization of the paste inside a hot press. At the moment of high pressure and temperature, the paste quickly fills all the voids and pores, thereby making the area on the sheet surface completely covered. The amount of flour in the paste recipe is 6.0-10.0%, depending on the viscosity of the resin.

Mimosa extract. Mimosa and its extract is a tannin. Its presence in the composition of the paste ensures the absence of shrinkage due to drying. That is, from the time the putty is applied to hot pressing, the putty without extract is able to shrink due to drying. Mimosa extract prevents this. It captures all the properties of each of the components and does not allow any of the parameters to stand out. If it is not possible to purchase this component, the analogue is Querbaho extract. Laboratory studies show almost identical properties; no industrial tests have been conducted. The amount of mimosa in the paste recipe is 1.0-2.0%.

The following terms are used to describe the method of making pasta:

- "cooking" - one portion of the prepared mixture. It is believed that the pasta is boiled.

- “glue machine” - a stainless metal or ceramic container equipped with an electric mixer and a tap for draining the cooked mass.

- “spatula” - a spatula made of thin plywood of different widths starting from 20mm.

To prepare the paste, you need to know that one portion (cooking) of the paste should be equal to 30 minutes of working with it. After 30 minutes, the composition is degraded (it dries).

Materials, tools and means of labor:

- glue maker (1 unit);

- consumable capacity (stainless steel bucket 3 l);

- a plastic container of 200 ml (for an employee employed on the putty of plywood);

- 25kg scales (with an accuracy of 1 gram per kg);

- blades, 10 pieces (of various widths);

- a blade 100 mm wide with a handle 500 mm;

- production thermometer for liquid media;

- offset paper (thin, transparent);

- paper tape;

- plywood 3 mm (300mm * 300 mm);

- viscometer (4 mm nozzle).

The method (order) of making pasta is as follows:

- pour resins SFZh 3013 or SFZh 3014 in an amount of 700-750 grams and a temperature of 20 deg.

- measure viscosity (measure viscosity strictly at a temperature of 20 degrees, the standard value is 65-75 seconds with a viscometer 4). At low viscosity add kaolin, at high viscosity add water.

- add chalk in an amount of 40-60 grams, mix.

- add mimosa extract 10-20 grams, mix.

- Add kaolin in an amount of 100-120 grams (add in small portions), mix.

- exposure 2 minutes (the mixer at this stage will no longer be able to work, continue mixing with a spatula with a long handle).

- add flour 60-100 grams, add flour in portions of 20 grams until the total viscosity reaches the state of "thick sour cream".

- excerpt 20 minutes

- mix the mass and make sure its viscosity (“thick sour cream” or “putty”).

- Pour into a consumable container and start manufacturing a new batch.

The technology (method) for the production of plywood using the declared paste is as follows.

Raw materials and logistics

The raw materials for the production of plywood are birch timber (plywood logs). The plants are supplied with raw materials by rail, road and water on ships.

Wood processing

Plywood raw materials are hydrothermally processed before veneering. Such processing increases the plastic properties of wood and creates the conditions for obtaining high-quality veneer. Hydrothermal treatment is carried out by boiling raw materials in cooking pools. The enterprises have outdoor pools of a cyclic type, as well as indoor pools of a continuous (passage) type.

Bucking of plywood raw materials

Timber for the production of peeled veneer is supplied to the mill in logs and churaks. Ridges after hydrothermal treatment are cut into chuk for peeling.

Peeling

Peeling is a process of cutting wood, in which a continuous strip of wood - veneer - is removed from a rotating chura by a progressively moving knife. This continuous tape with the help of scissors is cut into a format and stacked in the feet, after which the veneer is fed for drying.

Veneer drying

Veneers are dried in roller dryers. The veneer is moved along the dryer by a system of twin rotating rollers. Passing the drying chamber, the veneer is dried to a moisture content of 6 ± 2%. Then it is cooled in a special chamber.

Veneer Sort

Veneers are sorted by grades: for the outer layers and for the inner layers, in accordance with the technological instruction. The technology of processing the sheet plastic with the declared paste allows you to process defects and defects in the structure of wood and thereby increase the tolerances for them in the sorting process. Table 2 shows the defects and regulatory values according to GOST and taking into account the use of the declared paste (tanchuk 2000).

Tab. 2

In the case of an insert on the sheet, filling with paste for the 3rd and 4th grade is possible.

All open and dropped knots can be filled with paste, thereby obtaining a third grade or basis for lamination.

Fixing veneers .

Veneer repair is a technological process of veneer refinement in order to increase its grade. The fix is as follows:

- removal of wood defects from veneer sheets followed by termination of these places with inserts from high-quality veneer;

- gluing end cracks with adhesive tape;

- fastening cracks with metal clips using a stapler.

Re-gluing veneer.

Sliced non-veneer veneer is fed to the notch (edge trimming). This operation is performed on a guillotine type machine. Then the chopped pieces are fed to the rib gluing line, where they are glued together with a polyvinyl acetate emulsion into a continuous tape, which is then cut into the desired format. Positioning equipment is also used to rib veneer. At the same time, the pieces are glued using PVA emulsion, a paper tape with an adhesive layer or a thermoplastic thread. Further, veneered veneer is used along with solid veneer as plywood layers.

Assembly of plywood packages.

It includes applying the adhesive layer to the veneer on the applicator machine by passing veneer sheets between the rotating adhesive drums and laying the veneer sheets in a certain sequence, depending on the grade and thickness of the plywood.

Bonding plywood.

Gluing of plywood is carried out hot in hydraulic presses withstanding certain temperature conditions, depending on the brand and thickness of plywood. Before hot pressing, plywood packages undergo cold pressing.

After cold pressing, the bag is disassembled sheetwise and with the help of vanes all of the above defects are putty with the declared paste.

Procedure

- clean the place of repair of the sheet sheet from dust and foreign bodies with compressed air;

- Moisten slightly with a damp sponge (optional);

- apply the required amount of paste with a spatula;

- strongly push into the defect and repeat it repeatedly;

- remove excess;

- apply offset paper over the repair area. If necessary, use masking tape;

- move the sheet to the pack and proceed to the next;

- immerse in a hot hydraulic press.

The paste polymerization mode is similar to the plywood pressing mode.

Glued plywood after 24 hours enters the edge trimming and grinding.

Edge trimming

It is made in order to give plywood certain geometric dimensions. The operation is carried out sheet-by-frame on through-type cutting-edge machines located one after another and producing pairwise filing of two parallel sheet edges.

Plywood grinding

It is used to smooth the surface of plywood and eliminate thickness variations, as well as to give the products a more attractive presentation. Only the highest and medium grades of plywood are sanded.

Plywood sorting

When sorting, the amount and defects of wood, processing defects, bonding strength, dimensions, warpability of the sheets are determined. Plywood sorters visually determine the sort of each sheet and reveal hidden defects: delamination, bubbles. Bubbles are determined by tapping the surface of the plywood with a wooden hammer or using automatic ultrasonic flaw detectors. Plywood with bundles is rejected. When sorting, manual refinement of plywood is also carried out in order to eliminate some defects, for example, grinding of individual places, filling cracks. Some plywood sheets are sent for re-trimming in order to eliminate defects that cannot be eliminated by sorting.

Lamination

At the final stage, a film is applied on a plywood sheet from two sides. Then the plywood is loaded into a multi-span press, in which at the same time 15–18 sheets of products can be located. Pressing, during which the film sets with the surface of the plate, is carried out for 4.5–10 minutes at a temperature of 130–136 ° С. The pressing time depends on the density of the film, the thickness of the plywood and the type of coating (smooth or mesh). Due to the film, plywood acquires additional protection against water, mechanical damage, and aggressive media.

Marking and packaging plywood sheets

Each plywood sheet is clearly marked in the form of a round stamp, applied with indelible paint. Stamps are applied in the right corner of the back of the plywood. All plywood is packaged in packages that ensure its integrity and safety upon delivery. Plywood is subject to protection from above and from below by covers and from sides by covers. Marking of packages is carried out with indelible printing ink and is applied on 2 opposite covers of the package.

Storage

Plywood is stored in a specially equipped warehouse of finished products and must be protected from external influences.

The claimed technology (method) is aimed at increasing the number of varietal veneer.

Proper application of the technology allows to increase the share of the third grade from 30% to 60%. The share of laminated plywood in the total production volume can be 100%.

Claims (8)

1. Filling paste for covering veneer defects, containing phenol-formaldehyde resin, chalk, flour, water, characterized in that the paste additionally contains kaolin and mimosa extract, in the following ratio, wt. %: Phenol formaldehyde liquid resin - 70.0-75.0 Wheat flour - 6.0-10.0 Chalk - 4.0-6.0 Kaolin - 10.0-12.0 Mimosa extract - 1.0-2.0 Water is the rest. 2. A method of manufacturing plywood, including gluing veneer sheets by hot pressing and covering defects of plywood with filling paste, characterized in that the covering of defects of plywood is done with hot curing paste according to claim 1, by layer-by-layer filling of defects of veneer sheets immediately before hot pressing.