EP2353818B1 - Method for impregnating a porous material - Google Patents

Description

The invention relates to a method according to the preamble of claim 1.

Man könnte auch vom gravimetrischen Wassergehalt sprechen:Such methods, also referred to as impregnation, serve to protect porous material, which is made of solid material with cavities, against penetrating moisture, which in the case of organic materials, such as e.g. As organic fiber materials and especially in wood, leads to biological rotting. This causes considerable damage when using lumber. The term moisture u is defined as the mass of the water contained in the material m _w , divided by the mass of the material without water m ₀ (dry): $u=\frac{m_V}{m_0}\mathrm{,}$

One could also speak of the gravimetric water content:

In question coming porous materials are especially all kinds of wood, which are very sensitive to rotting. Only special tropical woods have even in the dead state sufficient self-protection against rotting. Other woods, such as in particular the native domestic timber in Germany, are very sensitive to the weather and unsuitable for outdoor use. Already the prevailing high humidity and rain load in Germany leads to the fact that the humidity in the wood rises to values above the fiber saturation point, which with typical domestic humidity For example, wood is about 12%, which allows the growth of wood-attacking microorganisms. The fiber saturation point is defined by the amount of moisture that can be absorbed by the fibers of the wood. In addition, moisture is stored in the voids between the fibers.

Dead wood is then protected against rot when it is dry or soaked with the growth of microorganism-preventing substances. Thus, many preservation methods dry the wood to a sufficiently low level of moisture and then seal it by surface coating or superficial soaking with waxes, paints, or the like to prevent the subsequent ingress of moisture.

It is also possible to prevent the rotting by soaking with mostly water-soluble poisons, which poisons are effective against the above-mentioned microorganisms. However, the problem here is, as with all impregnation method, the low penetration depth and also the environmental impact. Larger, inner areas of the wood remain unprotected and can rot with ingress of moisture.

As impregnating agents are e.g. aqueous solutions containing, for example, poisons or chemical reagents that chemically modify the wood and thereby make them more stable and rot-less. A process of the latter type is marketed by BASF under the name Belmadur. Pressure impregnation with tar-like toxic substances is also one of the known processes (railway sleepers), as well as the chemical treatment by acetylation.

The impregnant may also be a gas, for example, a monomer which is polymerized upon penetration into the wood.

A fundamental problem with all methods of impregnating porous material is the difficult introduction of the impregnant into the volume of the porous material so that it is impregnated as much as possible.

Many known methods have the liquid saturant sucked into the porous material capillary. Capillary suction, however, is very time consuming and, as a result, unreliable. It also requires that both the material and the impregnant have sufficient capillary properties.

There are very complex ways to improve the suction of wood, for example by needles and slits. The WO 99/64213 shows a method by irradiation with high frequency to make the wood better permeable and soakable.

Penetration of a drench into porous material, such as wood, can be enhanced by increasing the external pressure. In pressure impregnation, the wood is pressurized in a boiler with the impregnant, whereby the impregnant is pressed into the wood. Likewise, it is also initially evacuated and then pressed, with the aim of initially reducing the pressure in the wood and then push in by means of overpressure impregnation. Such methods are very complex and usually still unsatisfactory in the effect, since the impregnation penetrates only in the near-surface volume range.

During pressure impregnation, the impregnant presses into the wood, but its internal cavities are not empty. Rather, there are water residues and of course air. Both must first be largely removed before a sufficient watering is possible. Water is usually removed by preliminary drying. The remaining air is removed by evacuation, but only partially succeed with industrial means. More than 20% of the air remains in the wood during an industrial vacuum and prevents the penetration of the impregnant.

An impregnation process is from the EP 1 862 278 A1 known. The wood to be impregnated in this process should be moist. It is brought into contact with impregnation and at temperatures of more than 100 ° C, the water is boiled in the wood to be expelled in this way. At the same time the watering agent should penetrate into the wood. Again, the transport of impregnant into the wood is carried out exclusively by capillary suction, the liquid transport is still hindered in the wood interior by the flowing in the opposite direction of steam. There is a constant pressure between the inside and the outside of the wood, or at times even overpressure inside the wood. The penetration of the impregnating agent is thus very slowly as a result. To some extent satisfactory this procedure works only with very fresh wood, which can suck well still capillary. Another disadvantage of such methods is that the impregnating agent applied to the porous material is constantly flowed through by steam emerging from the wood. Of the steam from the wood brought impurities of all kinds, such. As resins, contaminate the impregnating agent, so that this can change its chemical and physical properties, such as the essential for the impregnation capillary action.

The WO 2009/040656 A2 , the US 5,970,624 and the DE-Auslegeschrift 2716157 describe generic soaking methods in which heat is applied to porous porous material comprising skeletal material having a boiling liquid to expel the boiling liquid from the material prior to impregnation. Thereafter, the material is brought into contact with the impregnant. It is still trying to penetrate of the impregnating agent by additional application of a vacuum in the material or an overpressure in the impregnating agent to improve.

The object of the present invention is to accelerate the impregnation in a generic method, while reducing the dependencies of the process of the material properties of the impregnation material.

This object is achieved with the features of the characterizing part of claim 1.

In the method according to the invention, the boiling liquid is first expelled by boiling from the porous material as in known methods in a container (which may also be a chamber). In contrast to known methods, however, the material is brought into contact with the impregnating agent only subsequently and immediately afterwards. The impregnating agent may in this case be a liquid or a gas, for example a monomer mixture which is polymerized after penetration into the wood. The contacting with the impregnating agent should take place so rapidly in distinction to the generic state of the art, that the vapor contained in the material is not significantly condensed to avoid disturbing sucking in ambient air.

The impregnation can generally take place entirely or predominantly by means of capillary action, but according to the invention takes place by reducing the temperature of the material or reducing the pressure in the material, or by a combination of both measures, except for values at which the liquid condenses in the material, and thereby superheated gaseous state passes into the wet steam state. In the simplest case, the material according to the invention is immersed in cold impregnant after the boiling process has been completed. "Cold" refers to the process temperature during the boiling process, and is in relation to this and to see the process pressure in relation. At the same process pressure, "cold" is actually lower temperature and preferably a temperature below the boiling point.

The material requires a sufficiently high initial moisture according to the method. It then arises when boiling sufficient steam in the material, so that the existing air is expelled from the steam. If dry material is to be processed, the material may need to be wetted in an upstream process step.

Now, if the impregnant is cooler than the boiling liquid in the vapor phase, then the vapor phase changes into a condensation phase. This condensation phase results in a volume decrease of the boiling liquid by a factor> 1000, which forms a vacuum in the material. As a result, the impregnating agent is sucked into the material, where, due to its lower temperature, the residual boiling liquid in the vapor phase is likewise converted into the condensation phase.

The suction process described above can be further accelerated by an increase in pressure in the watering agent.

By lowering the ambient pressure in the container during the boiling step, the temperature required for boiling can be lowered, since pressure and temperature are coupled together in the boiling range. This allows a gentle treatment of the skeletal material.

Bringing water (or another liquid) to evaporate by boiling is very energy-consuming due to the high boiling enthalpy. An improvement in the energy and time efficiency of the process can be achieved according to claim 5 and 6, by the water in the material is not uniform, but along the Fiber direction is brought to boiling from inside to outside. The vapor pressure generated in the interior of the material then drives the still liquid water in the outer areas out of the material on its way outwards, while at the same time heating it up. This expelled water then does not need to be vaporized. Through the temporal and spatial change of the heating power over the material geometry, the boiling process can be optimized, for example, in terms of time and energy.

After the boiling liquid has been expelled from the material, the material is incorporated into the e.g. brought by a separator or lock separated impregnating container (which may also be a drinking chamber) and immersed in the impregnation. Alternatively, it is also possible to introduce the impregnating agent directly into the boiling container (or the boiling chamber) after the boiling process. The material is empty except for the remaining liquid vapor and can now take up large amounts of impregnating agent, with the remaining boiling liquid condensing again from the superheated gas state, thereby reducing its volume from the gaseous to the liquid state to less than 1/1000 of the original gas volume.

The most suitable liquids which can be boiled are the water contained in the wood, but also other liquids, e.g. Acetone, which can be introduced into dry material, or in exchange for existing water. However, water is taken as an example in the description without restriction of generality

The boiling process can take place without further control over a certain period, for example. However, preference is given to working according to claim 2 to a residual moisture in the material in the range, preferably below the fiber saturation of the wood. Then the residual moisture is below the limit, where the wood rots.

Preferably, according to claim 3, is further dehumidified to the residual moisture in the vicinity of 0th

The heat during boiling can be done in a suitable manner. Relatively well suited would be e.g. a hot steam or hot air heating, or the use of heat radiators. However, as with most other heating options, the material is only heated from the surface, so that the boiling range only slowly penetrates from the outside into the core area. Advantageously, therefore, the features of claim 4 are provided. High frequency (e.g., microwave heating) and ultrasonic heating are volume heating methods that also apply heat directly to the core area of the material so that it dries quickly and completely from the inside.

The moisture content of the material should be checked continuously during the boiling process in order to determine when the desired or still tolerated residual moisture is reached. Preferably, according to claim 7, the moisture is determined by weighing the material. This is a simple and highly accurate procedure. It can be used to determine the moisture content of the material and also during impregnation to determine the degree of soaking in order to stop the soaking after reaching a desired value. The soaking process can also be used e.g. over a certain period of time, which is considered sufficient.

In the following, a preferred embodiment of the method according to the invention will be described. It is poplar wood impregnated with a resin impregnant, which is, for example, a two-component resin with sufficiently long pot life, which can penetrate liquid, and then harden in the wood.

Here, optionally, the moisture of the wood is optionally checked, and if this is considered insufficient by appropriate measures to a more appropriate value can be increased. Then the wood is heated, taking into account the process pressure, to a temperature at which the moisture contained boils. Preferably, a high frequency heating is used, which heats quickly and in the entire volume. When heating and boiling according to the invention, there is no contact between the material and the impregnating agent to avoid contamination of the impregnating agent.

The wood is constantly subjected to a weighing, in which the total mass, consisting of wood and water, is measured. From the measured weight curve it can be determined from the relative weight loss, when the wood has the desired residual moisture of e.g. maximum fiber saturation or, if desired, even zero. Then the boiling can be stopped.

Then the wood is first while maintaining the temperature and the process pressure, z. B. in a container in which serving as impregnation liquid resin and completely brought by submersion in contact with this.

In this case, preferably, the temperature of the impregnant is so low that, taking into account the process pressure, the vaporized water (or any other liquid present in the wood) condenses again in the wood. During condensation, the volume of the water reduces from less than to less than steam 1/1000. It thus creates a condensation vacuum in the wood, which sucks the surrounding resin at high speed into the wood. This process can be further accelerated by applying an external process pressure.

Also in this impregnation process, the wood may preferably be monitored by weighing until the resulting weight increase of the wood during soaking indicates the desired degree of soaking. Then the impregnation process can be terminated by removing the wood.

Claims (9)

1. Method for impregnating a porous material, which contains a liquid that is capable of boiling, consisting of solid matrix material with hollow spaces, with a gaseous or liquid impregnating means, whereby the liquid that is capable of boiling is evaporated from the material by boiling before impregnating while supplying heat, whereby the material is heated sufficiently for the liquid that is capable of boiling to boil at the existing process pressure, whereby the boiling process is maintained until a desired residual moisture content is attained, whereby the material is then immersed completely in the impregnating means until a desired degree of impregnation is attained, characterised in that the impregnating means is maintained at a pressure and a temperature below the condensation line and dew line, respectively, at which the liquid that is capable of boiling condenses, whereby the immersion occurs so close in time after the boiling step that the liquid that is capable of boiling is predominantly still present in the material in the vapour phase such that a condensation vacuum arises in the material.
2. Method according to any one of the preceding claims, characterised in that the boiling process is continued until a residual moisture content below the fibre saturation is attained.
3. Method according to claim 2, characterised in that the boiling process is continued until a residual moisture content of approximately zero is attained.
4. Method according to any one of the preceding claims, characterised in that the heat for boiling is supplied through infrared, hot air, hot vapour, high frequency or ultrasound heating.
5. Method according to claim 4, characterised in that the heat is supplied to the interior of the material first.
6. Method according to any one of the preceding claims, characterised in that the supply of heat proceeds from inside out following the direction of the fibres.
7. Method according to any one of the preceding claims, characterised in that the material is checked for moisture content and/or degree of impregnation through weighing the material.
8. Method according to any one of the preceding claims, characterised in that the boiling process proceeds at reduced process pressure.
9. Method according to any one of the preceding claims, characterised in that the impregnation process proceeds at increased process pressure.