HK1083209A - Process for the production of polyurethane molded articles - Google Patents

Description

Process for producing polyurethane molded article

Technical Field

The present invention relates to a process for the production of Polyurethane (PU) moldings, in particular PU sandwich components, and their use.

Background

The production process of sandwich elements for the manufacture of flat panels is known for some time. The sandwich construction consists of a light and compression resistant core and a high strength cover. This composite structure is formed from a PU reaction mixture that, when applied on both sides in a hot compression molding process, can form a strong bond. The inner core of the sandwich structure is preferably composed of a honeycomb-structured cardboard, which serves as a spacer for the covering layer wetted with PU during the compression process. The wetting of the sandwich cover layer is preferably carried out by spraying. Since with this orientation the two-sided application can be carried out simultaneously, the substrate carrier is in this case robot-guided, and the top cover is arranged in a horizontal or preferably vertical direction during the PU application by mixing. Also, the polyurethane mixing head may be guided by a robot.

Three-dimensional molded articles can also be produced due to a combination of compression and forming processes. The honeycomb core, which is built up to a uniform thickness of a few tenths of a millimeter over the entire surface for the sheet material, is now compressed in partial areas to a small percentage of its original dimensions. The shaping of the outer contour of the finished component is carried out by clamping the edge in a shaping tool (mold) by a sandwich of sandwich structures, so that the structural component closes the outer edge after removal from the mold. In this forming process, a three-dimensional structural component is obtained having an unlaminated visible surface and also unlaminated visible edges.

Previous production methods of PU molded articles, in particular PU sandwich regions, provide three-dimensional parts with poor edge definition and/or insufficient material filling. Especially in the case of highly profiled articles, the edge definition is often unsatisfactory. Furthermore, the amount of polyurethane that can be applied is limited, since the applied liquid polyurethane mixture tends to drip.

Disclosure of Invention

It is an object of the present invention to provide a process which enables three-dimensional PU articles with good edge definition to be produced in a simple manner.

This object is surprisingly achieved if a gas is added to the applied polyurethane mixture and a foam stabilizer is also included.

Drawings

FIG. 1 illustrates a molded article produced by the process of the present invention as described in example 1.

FIG. 2 illustrates a molded article produced from the prior art as described in example 2.

Fig. 3 is a photograph in which a molded part produced according to the inventive process described in example 3 (designated section B) was arranged next to a molded part produced according to the prior art described in example 4 (designated section a).

The invention relates to a process for the production of polyurethane moldings, in which

a) The polyurethane-forming mixture is added to the reinforcing-fiber layer of the sandwich of at least one core layer (inner layer) and two covering layers of reinforcing fibers or to the reinforcing-fiber mat,

b) placing the sandwich or reinforcing fibre mat from a) in a mould,

c) shaping the mold contents at a molding temperature of from 40 ℃ to 160 ℃ and simultaneously curing the polyurethane forming mixture to form a molded article,

d) removing the molded article produced in c) from the mold, and

e) optionally, post-treating the molded article.

At least some portion of the polyurethane-forming mixture added to the reinforcing fiber covering or reinforcing fiber mat must have added thereto a gas and also contain a foam stabilizer. Molded articles with good edge definition are obtained by this process. Furthermore, it is possible to increase the amount of polyurethane in proportion to the application surface and to prevent or at least minimize running out or dripping.

In a preferred embodiment of the process according to the invention, in addition to the polyurethane mixture, the chopped fibers are also applied to the component or to the entire surface of the reinforcing fiber covering or reinforcing fiber mat. A combination of these additionally applied chopped fibers wetted with PU was carried out.

Air, nitrogen and CO₂Is the gas preferably used.

The introduction of the gas can be carried out by any known method, such as a batch or in-line method.

Suitable foam stabilizers include those known to those skilled in the art. Examples of particularly preferred foam stabilizers are polyether siloxanes, in particular those which are water-soluble. The preferred stabilizer compounds are synthesized in such a way that the copolymer of ethylene oxide and propylene oxide is bonded to the polydimethylsiloxane residue. Such foam stabilizers are described, for example, in U.S. patents 2834748, 2917480 and 3629308. Of particular interest are polysiloxane-polyoxyalkylene copolymers which are multi-branched by allophanate groups, such as those described in DE-OS 2558523. Also suitable as foam stabilizers are other organopolysiloxanes, oxyethylated alkylphenols, oxyethylated aliphatic alcohols, paraffin oils, castor oil esters and ricinoleates, turkey red oil and peanut oil, and cell regulators (cell regulators) such as paraffins, aliphatic alcohols and dimethylpolysiloxanes. For improved emulsification, cell structure and/or stabilization, oligomeric polyacrylates employing polyoxyalkylene residues and fluoroalkane residues as side groups may be used. The foam stabilizers are generally used in amounts of from 0.01 to 5 parts by weight per 100 parts by weight of polyol.

The polyurethane-forming mixture used in the process of the present invention generally comprises

A) At least one polyol component having an average OH number of 300-700, comprising at least one short-chain and one long-chain polyol, the individual polyols having a functionality of from 2 to 6,

B) at least one polyisocyanate,

C) optionally, a blowing agent,

D) an activator, and

E) optionally auxiliary substances, mould release agents and additives.

Suitable polyols that may be included in the polyol component are polyols containing at least two H atoms reactive with isocyanate groups. Polyester polyols and polyether polyols are preferably used.

According to the invention, preference is given to using higher nuclear isocyanates of the diphenylmethane diisocyanate series (pMDI type), their prepolymers or crude MDI.

As blowing agents C) it is possible to use compounds which act chemically or physically. As chemically acting blowing agents, preference may be given to using water, which forms carbon dioxide by reaction with isocyanate groups. Examples of physical blowing agents are (cyclo) aliphatic hydrocarbons, preferably those containing from 4 to 8, more preferably from 4 to 6 and most preferably 5 carbon atoms, partially halogenated hydrocarbons, or ethers, ketones or acetates. Foaming may also be achieved by adding compounds that decompose at temperatures below room temperature and release of gases. The various blowing agents can be used individually or in a mixture with respect to one another.

Suitable catalysts include conventional activators for the foaming and crosslinking reactions, such as amines and metal salts.

Other auxiliary substances, mold release agents and additives may optionally be introduced into the reaction mixture. Examples of such additives include surface-active additives such as emulsifiers, flame retardants, nucleating agents, antioxidants, lubricants and mold release agents, colorants, dispersion aids and pigments.

The isocyanate and polyol components are generally reacted in such amounts that the ratio of the equivalents of NCO groups of the polyisocyanate to the total equivalents of hydrogen atoms of the remaining components reactive with isocyanate groups is from 0.8: 1 to 1.4: 1, preferably from 0.9: 1 to 1.3: 1.

The core layer is preferably a thermoformable polyurethane foam, paper, metal or plastic honeycomb. Suitable fibrous materials include glass fiber mats, glass fiber nonwovens, glass fiber random structures, glass fiber tissue, chopped or milled glass or mineral fibers, natural fiber mats and woven fabrics, chopped natural fibers and fiber mats, fiber nonwovens and woven fabrics based on polymer fibers, carbon fibers or aramid fibers, and mixtures thereof.

The sandwich used in step a) is normally produced in such a way that cover layers of reinforcing fibers are applied to both sides of the core layer. The polyurethane is then added to form a two-component mixture (the so-called isocyanate and polyol components). It may also be preferred to apply the chopped fibers over all or part of the surface while the polyurethane is added to form the mixture.

If a mat of reinforcing fibres is used in step a), the mat is first taken up and impregnated in a conventional manner with a polyurethane-forming mixture. In this case, two types of chopped fibers may be additionally applied simultaneously over the entire or part of the surface.

The PU moldings produced according to the invention, after removal from the molding, can be laminated in a subsequent step with a covering or decorative substance according to known processes. If a suitable covering or decorative substance is used, the bonding to the PU molded article can already take place during the production step by first taking the covering or decorative substance and simultaneously compressing it with the sandwich structure or the reinforcing fibers in the mold. As decorative materials, textiles closed by polyurethane impregnation, compact or foamed plastic films, and spray skins (skins) or RIM skins of polyurethane can be used in this connection. As covering layer, it is also possible to use preformed materials suitable for external applications, such as metal foils or sheets, and also compact thermoplastic composites of PMMA (polymethyl methacrylate), ASA (acrylate-modified styrene-acrylonitrile terpolymer), PC (polycarbonate), PA (polyamide), PBT (polybutylene terephthalate) and/or PPO (polyphenylene oxide) in painted, paintable or colored form. Continuous or batchwise produced coatings based on melamine-phenol, phenol-aldehyde, epoxy or unsaturated polyester resins can likewise be used as coatings.

Detailed Description

The PU moldings produced according to the invention are preferably used as structural components or linings/cladding parts, in particular in the automotive industry, the furniture industry and the construction and construction industry. The invention is discussed in more detail with the aid of the following examples.

Examples

Starting materials:

polyol 1: OH number 865, polyether polyol produced by adding PO to trimethylolpropane.

Polyol 2: a polyether polyol having an OH value of 1000 produced by adding PO to trimethylolpropane.

Polyol 3: a polyether polyol having an OH value of 42 produced by adding 86% PO and 14% EO to propylene glycol as a starting material.

Polyisocyanate: polymeric MDI having an isocyanate content of 31.5% by weight and available under the name Desmodur 44V 20L from Bayer Material Science AG.

A stabilizer: silicone stabilizers, available under the name Polurax * SR 242 from OsiCrompton Witco Specialities, D60318Frankfurt, Humoldstr.12.

Catalyst: AN amine catalyst available under the name Thancat * AN10 from Air products GmbH, D-45527 Hattingen.

Colorant: baydur * Black paste DN, available from Bayer Material Science AG.

Polyurethane formulation:

formulation 1:

component A
			Polyol 1	30.0	Parts by weight
Polyol 2	20.0	Parts by weight
			Polyol 3	33.0	Parts by weight
Catalyst and process for preparing same	2.8	Parts by weight
			Stabilizer	1.3	Parts by weight
Acetic acid	0.3	Parts by weight
			Water (W)	1.4	Parts by weight
Coloring agent	3.3	Parts by weight
			B component
Polyisocyanates	140.0	Parts by weight

The average OH number of the polyol mixtures (polyols 1, 2 and 3) was 568mg KOH/g.

Formulation 2:

component A
			Polyol 1	30.0	Parts by weight
Polyol 2	20.0	Parts by weight
			Polyol 3	33.0	Parts by weight
Catalyst and process for preparing same	2.8	Parts by weight
			Acetic acid	0.3	Parts by weight
Water (W)	1.4	Parts by weight
			Coloring agent	3.3	Parts by weight
B component
			Polyisocyanates	140.0	Parts by weight

The average OH number of the polyol mixtures (polyols 1, 2 and 3) was 568mg KOH/g.

Example 1(according to the invention)

Addition of gaseous CO to the A component of formulation 1 using a hollow shaft stirrer of star type₂. After the addition, 420kg/m are measured by liter metering³The polyol density of (a).

The broken glass fiber is adopted to be 450g/m²Applied to both sides of a core layer consisting of corrugated cardboard 5/5 type 10mm thick paper honeycombs and used in a total amount of 450g/m at room temperature²By addition of CO₂Polyurethane formulation 1 of (a) was spray coated.

This sandwich was placed in a sheet forming die into which a sharp-edged flat piece of steel of dimensions 6 x 30 x 300mm was previously inserted for forming. The sandwich was then compressed to a wall thickness of 9.8mm, heated to 130 ℃ in a mold, and compressed more strongly to a wall thickness of 3.8mm in the region of the planar steel insert.

The more strongly compressed regions have sharp edge definitions as shown in fig. 1.

Example 2(comparison)

The experiment described in example 1 was repeated, with the difference that no CO was added to the formulation₂。

The more strongly compressed regions have defective edge definitions as shown in fig. 2.

Example 3(according to the invention)

Addition of gaseous CO to polyurethane-forming formulation 1 as in example 1₂。

The broken glass fiber is adopted to be 450g/m²Applied to both sides of a core layer consisting of corrugated cardboard 5/5 type 40mm thick paper honeycombs and used in a total amount of 550g/m at room temperature²By addition of CO₂Polyurethane formulation 1 of (a) was spray coated. Furthermore, chopped glass fibers of type 816, 2400 tex/Muhlmerier were applied by a cutter, type SW 2/wolffangel, during spraying, in the subsequently formed area.

This sandwich was placed into a sheet forming die which allowed the formation of a cylindrical dome of 35mm height, 50mm diameter by a corresponding depression in the upper portion of the die. The sandwich was then compressed to a wall thickness of 17mm and heated in a mold to 130 c, corresponding to areas of less significant compression of the dome.

The dome is formed with a closed surface as shown in fig. 3, section B.

Example 4(comparison)

The experiment described in example 3 was repeated, with the difference that no CO was added to formulation 1₂And without adding additional glassGlass fibers.

The dome is formed with an open, unwanted surface as shown in figure 3, section a.

Example 5(comparison)

The experiment described in example 3 was repeated, but without addition of CO to formulation 1₂。

Due to the poor adhesion behavior of the polyurethane mixture, the additionally applied chopped glass fibers fall down until the intercalation of the sandwich into which the polyurethane is added.

Example 6(comparison)

The experiment described in example 1 was repeated, except that formulation 2 was used instead of formulation 1.

The more strongly compressed regions have defect edge definitions (similar to that shown in fig. 2).

Although the invention has been described in detail in the foregoing section for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims (8)

1. A method for producing a polyurethane molded article, comprising:

a) adding a polyurethane-forming mixture comprising a foam stabilizer and a gas to a part comprising (1) a sandwich comprising at least one core layer and two cover layers of reinforcing fibers or (2) a mat of reinforcing fibers,

b) placing the part from a) in a mould,

c) maintaining the mold at a temperature of 40 ℃ to 160 ℃ to form a mixture of the molded part and the hardened polyurethane and thereby form the molded article,

d) removing the molded article produced in c) from the mold, and

e) optionally, post-treating the molded article.

2. The method of claim 1, wherein chopped fibers are also added to at least a portion of the part during step a).

3. A structural component of an automobile comprising the molded article produced by the method of claim 1.

4. An automotive liner comprising a molded article produced by the process of claim 1.

5. A structural component of a building comprising the molded article produced by the method of claim 1.

6. A structural component of an automobile comprising the molded article produced by the method of claim 2.

7. An automotive liner comprising a molded article produced by the process of claim 2.

8. A structural component of a building comprising the molded article produced by the method of claim 2.