NL9200658A - Method for fabricating a panel composed of a core of polyurethane which on the outside(s) is covered by a covering layer, and panels thus obtained - Google Patents

Abstract

The invention relates to a method for fabricating a panel composed of a core of polyurethane which on the outside(s) is covered by a covering layer, the core being fabricated from a fine, granular material of polyurethane, provided with a binder, by compression at elevated temperature and pressure. The covering layer is simultaneously pressed onto the core while the core is moulded into panel shape, the temperature increase while the core panel is being formed takes place gradually and the pressure build-up is carried out in phases.

Description

Short indication: Method for manufacturing a plate built from a core of polyurethane which is covered on the outside (s) with a coating and plates thus obtained.

The invention relates to a method for manufacturing a plate built from a core of polyurethane which is covered on the outside (s) with a coating. The invention further relates to the plates thus obtained.

Dutch patent application 7001834 discloses a method for manufacturing polyurethane plates which are provided with a coating, which coating material is applied by spraying. This method can be carried out continuously, but the equipment to be used therewith is relatively expensive. It has now been found possible to simplify the method and device considerably.

U.S. Pat. No. 3,904,336 discloses a coated sheet, the core material of which is wood chips and / or cellulose fibers, which compressed sheets are commonly known as wood fiber sheets. The coated sheets are produced in several steps, the core material being manufactured in the first step, and the laminate is then applied to this core material, the core forming temperature being substantially maintained prior to the application of the laminate.

It is known from Dutch patent application 6808556 to produce plates from polyurethane granules which are processed into a plate by providing the granules with an isocyanate-containing binder in an amount of about 6% by weight, calculated on the polyurethane material and then at elevated temperature and press the material compressed into the plate. A veneer of known types of wood can be applied to this as a coating. It has now been found possible to obtain a better adhesion between the polyurethane core and the coating to be applied. Further details about the manufacture of the core material consisting of polyurethane by starting from polyurethane granules which are provided with isocyanate can be derived from the Belgian patent specification 881.761 or from the corresponding European patent application 37.860. It is indicated therein that the binder is added in an amount of 3 to 6% by weight, the compression takes place under a pressure of 15-20 kg / cm 2 and the temperature is kept at about 190-210 ° C. However, this European patent application 37,860 does not provide any further information about the application of a coating on such a core plate of polyurethane. The present patent application is aimed at the latter aspect.

A method for manufacturing polyurethane plates, which starts from polyurethane granules, to be regarded as waste material, is also known from European patent application 338.047. Thereby, the polyurethane plate is manufactured in two steps, i.e. a first step (pre-pressing) which is carried out at a pressure of at most 20 kg / cm2 and a temperature of about room temperature, while in a second step compression is carried out at a pressure of not more than 40 kg / cm2 and a temperature lower than 170 ÖC. According to this European patent application 338,047, different types of polyurethane foam can be used, such as a hard polyurethane foam and / or an integral foam. Optionally, a reinforcing fiber layer is applied in the plate to improve the flexural strength, but no further information can be derived from this patent application about the application of layers on the outside. If plates are manufactured that are coated on the outside, usually to embellish the outer shape or to obtain water-repellent properties and the like, the plate-shaped core material is first manufactured and then the coating is applied with glue or by spraying the coating material allow the core material and the material to be sprayed to harden.

It has now been found possible to obtain a better adhesion between the outer layer to be applied and the core material by applying a method according to the invention and this is characterized in that the core is made of a fine granular core material of polyurethane, provided with a binder. by compression at elevated temperature and pressure, simultaneously pressing the coating on the core while the core is brought into the plate form and the temperature increase in the formation of the core plate occurs gradually and the pressure build-up is carried out in phases.

Thus, not only is the coated sheet formed in one operation, but very good adhesion is obtained between the coating and the core material, because the coating is applied as a substantially "chemically bonded" layer.

Preferably, the top layer is formed from polyester, for which a prepreg is used as the starting material, which is a polyester material that flows out and is hardened after raising the temperature and pressure.

The starting material for the core is polyurethane foam which is commercially available as waste material in the form of blocks. These blocks or briquettes about 1 dm3 in size are ground into a sawdust-like material which is passed through a sieve of about 10 mm. The average main fraction of the sawdust-like material is about 2 mm. This material is the starting material for manufacturing the core of the plate. Shortly before the plates are manufactured, the sawdust-like material of polyurethane is sprinkled on an aluminum plate, which plate forms part of the device for forming the end product. A sheet of paper is first placed on the aluminum plate and this is provided with a prepreg polyester foil. The sawdust-like polyurethane material is sprinkled on the prepreg polyester film to a thickness of approximately 7 cm, depending on the desired thickness of the end product. This layer is covered with a second prepreg foil and a second sheet of paper is then placed on it. These assemblies are fed to an oven in which the final product is formed. The oven is preferably designed in such a way that several plates can be formed one above the other, so that, for example, in one operation 12 plates are formed with dimensions of 2.50 x 1.20 m, which plates vary in thickness from 1 to 3 cm.

The assemblies are fed to the oven which has been heated to a temperature of about 190 ° C. Once the assemblies are inserted into the oven, they are gradually heated to a temperature of about 190 ° C and immediately after the assemblies are introduced into the oven, the pressure is increased by compressing the assemblies using a top and bottom punch . The pressure build-up exerted on the assemblies takes place in three steps, reaching the final pressure of 25 kg / cm2 in about 3 minutes. Within a minute the pressure is increased to about 2 kg / cm2, in a second step the pressure is increased to about 15 kg / cm2 and in the last step the final value of 25 kg / cm2 is reached, which value is reached after about 3 minutes and then maintained for 6 minutes. During the pressure build-up, the temperature of the assembly is increased, reaching the final temperature of 190 ° C on the surface within about 1 minute. At the core of the assembly, the temperature is significantly less than 190 ° C and it will be appreciated that depending on the thickness of the plate to be obtained, the interior of the plate to be obtained will only reach the final temperature of 120 ° C after approximately 7 minutes. to achieve.

After a period of 9 minutes, the resulting plates are released by sliding the plates out of the oven so that the oven can be refilled.

The furnace is heated by the fact that the furnace is provided with steel supports on which the assemblies are placed, mounted on the aluminum plate, which steel supports are internally piped through which heated oil is pumped at a temperature of 190 ° C. It is of course also possible to heat the steel supports in other ways.

By the interaction of temperature increase, pressure build-up and the choice of the core material and the covering layer to be applied, a sandwich structure is obtained, the covering layer of which forms a whole with the core. This can be clearly seen from a cross-section of the obtained sheet, in which the cover layer, which is completely smooth on the outside, is pressed into the core material with an irregular pattern, so that a good anchoring is obtained between the polyester layer and the polyurethane-containing core material.

With regard to the pre-processing of the assembly which is placed in the oven, it should be noted that the spraying of the sawdust-like polyurethane material with polyisocyanate must not take place longer than a few hours before the compression, because otherwise a reaction can already start. Further details about the amount of isocyanate to be used as a binder can be derived from Belgian patent specification 881, 761, mentioned in the opening paragraph. It will also be clear that the amount of isocyanate to be used depends on the final temperature in the oven. The polyester primer film to be applied to the sawdust-like polyurethane material can have a smaller surface area than the end surface of the obtained plate, because during compression the film becomes thinly liquid and spreads over the surface. Since the oven consists of an open system, it is recommended that the prepreg foil is not chosen too large because otherwise the polyester material could flow out of the oven. Due to the gradual liquefaction of the prepreg film, a gradual absorption also takes place through the densifying core of the liquefying film material, so that the chance of waste being formed is small. By the correct choice of the size of the prepreg foil it can be achieved that at the end of the pressing operation the foil exactly reaches the outer surface of the core material.

After removal from the oven, the obtained plate only needs to be post-processed by lightly sanding the paper, after which a plate to be used immediately is obtained from a polyurethane plate consisting of a polyurethane core provided with highly adhering polyester layers.

The plates manufactured according to the invention are very suitable for laying floors and walls, especially in a wet environment, because the plates are highly resistant to moisture and have high impact resistance values. They are also suitable as formwork material due to the suitable mechanical properties.

Claims (5)

Method for manufacturing a plate built from a core of polyurethane which is covered on the outside (s) with a coating, characterized in that the core is made of a fine, granular material of polyurethane, provided with a binder by compression at elevated temperature and pressure, simultaneously pressing the coating on the core while the core is brought into the plate form and the temperature increase in the formation of the core plate occurs gradually and the pressure build-up is carried out in phases. Method according to claim 1, characterized in that a polyester coating is applied. Method according to claims 1-2, characterized in that a temperature of 190 ° C is reached when the starting materials are compressed. Method according to claims 1-3, characterized in that the pressure build-up takes place in three phases, i.e. within about 1 minute a pressure of about 2 kg / cm2 is reached, after 2 minutes a pressure of about 15 kg / cm2 and after 3 minutes a maximum pressure of about 25 kg / cm 2, which pressure is then maintained for another 6 minutes. Plate consisting of a polyurethane core and a polyester coating, characterized in that the plate is manufactured according to a method described in claims 1-4.