EP2010581A1

EP2010581A1 - Use of carboxyl-functional polyvinyl acetates for producing bmc parts

Info

Publication number: EP2010581A1
Application number: EP07728208A
Authority: EP
Inventors: René GRÄWE
Original assignee: Wacker Chemie AG
Current assignee: Wacker Chemie AG
Priority date: 2006-04-27
Filing date: 2007-04-18
Publication date: 2009-01-07
Also published as: CN101432323A; DE102006019686A1; JP2009534508A; US20090182090A1; WO2007125035A1

Abstract

The invention relates to the use of carboxyl-functional polyvinyl acetate solid resins as additives in formulations without thickeners for producing BMC parts.

Description

Use of carboxyl-functional polyvinyl acetates for the production of BMC moldings

The invention relates to the use of carboxyl-functional polyvinyl acetate solid resins for the production of BMC moldings.

Unsaturated polyester resin compositions (UP resins) are frequently used in the production of sheet-like plastic parts. These polyester resins are reaction products of a dicarboxylic acid or a dicarboxylic acid anhydride with a polyol. Such polyester resin compositions also contain a monomer having ethylenically unsaturated groups, generally styrene. Styrene is added to the polyester resin composition to dissolve the polyester and to ensure that the polyester composition is a flowable mass. To reinforce the plastic parts obtained with the polyester resin composition, the polyester resin compositions still contain fiber materials such as glass fiber, carbon fiber or corresponding fiber mats.

The problem with the processing of such polyester resin compositions (Fiber Reinforced Plastic Composites = FPR composites) is the volume shrinkage during the heat curing of the polyester resin. To reduce the shrinkage in the

Curing of the polyester resin therefore this so-called low-profile additives are added. The low-profile additive reduces shrinkage during curing, reduces residual stresses, reduces micro-cracking and facilitates compliance with manufacturing tolerances. The low-profile additives are thermoplastics such as polystyrene, polymethyl methacrylate and in particular polyvinyl acetate. Polyvinyl acetates having up to 1% by weight of carboxyl-functional comonomer units are also used. At higher levels of carboxyl functional comonomer units, shrinkage reduction is unsatisfactory. Two methods for the production of thermoset moldings from FRP composites are BMC technology (BuIk Molding Compound) and SMC technology (Sheet Molding Compound). In the SMC process, a pasty mass of styrenic polyester resin solution, low profile additive, crosslinking catalyst, filler, mold release agent and optionally other additives is prepared, which is applied to a polyamide film. Subsequently, fiberglass is sprinkled on this layer, and finally applied another layer of the pasty mass. This sheet sandwich is then peeled from the film, cut into pieces and pressed using pressure and temperature to form parts.

In the BMC process, the constituents of the compound, the styrenic polyester resin solution, the low profile additive, the crosslinking catalyst, filler, mold release agent and optionally other additives are mixed to a pasty mass, then admixed with glass fiber, and then using pressure and temperature the molded part manufactured.

For the BMC process currently non-functionalized solid polyvinyl acetate resins are used as low-profile additives. The disadvantage here is that the addition of fillers which reduce the cost of the formulation is limited by the relatively high intrinsic viscosity of styrenic polyvinyl acetate solutions. For the SMC process it is known from EP 501176 A1 that thickening of curable polyester resin molding compositions can be accelerated by addition of thermoplastic vinyl polymers containing acid groups. The use of vinyl acetate

Acrylic acid copolymers in formulations with thickening agents is also described in DE-OS 2104575.

It was therefore an object to find a way that allows the incorporation of larger amounts of filler in the formulation of molding compositions for the BMC process. Surprisingly, it has been found that carboxyl-functional polyvinyl acetate solid resins, with the same molecular weight, result in styrenic solutions with significantly lower intrinsic viscosity, which makes it possible to incorporate higher amounts of fuel.

The invention relates to the use of carboxyl-functional polyvinyl acetate solid resins as an additive in formulations without thickening agents for molding compositions for the production of BMC molded parts.

Suitable comonomers having carboxyl groups for the preparation of carboxyl-functional polyvinyl acetate solid resins are simply ethylenically unsaturated mono- and dicarboxylic acids. Preference is given to acrylic acid, methacrylic acid, fumaric acid, crotonic acid. Particularly preferred is crotonic acid. The proportion of comonomer units having carboxyl groups in the polyvinyl acetate solid resin is from 0.5 to 10% by weight, preferably greater than 1% by weight up to 10% by weight, particularly preferably from 3 to 10% by weight. , in each case based on the total weight of the solid polyvinyl acetate resin.

The preparation of the carboxyl-functional polyvinyl acetate solid resins is carried out in a known manner by the mass, suspension, or preferably solution polymerization process. Suitable solvents are, for example, monohydric, aliphatic alcohols having 1 to 6 C atoms, preferably methanol, ethanol, propanol, isopropanol. Particularly preferred are ethanol and isopropanol. The reaction is generally carried out under Ruckflußbedingungen, generally at a polymerisation sation level of 40 ⁰ C to 140 ⁰ C, carried out to the

Siedekuhlung to dissipate the heat of reaction to use. This can be done at atmospheric pressure as well as under slight overpressure.

The initiators used are organic peroxides or azo compounds. Suitable examples include diacyl peroxides such as dilauroyl peroxide, peroxo esters such as t-butyl peroxypivalate or t-butyl peroxo-2-ethylhexanoate, or peroxodicarbonates such as ethyl peroxodicarbonate. The amount of initiator is generally from 0.01 to 5.0 wt .-%, based on the monomers. The initiators can both be submitted and metered. It has proven useful to submit part of the required amount of initiator and to dose the remainder continuously during the reaction.

The adjustment of the molecular weight can be carried out in a manner known to the skilled worker by polymerization in the presence of molecular weight regulators. Suitable regulators are, for example, alcohols such as ethanol or isopropanol, aldehydes such as acetaldehyde or propionaldehyde, silane-containing regulators such as mercaptosilanes, for example 3-mercaptopropyltrimethoxysilane.

The polymers can be prepared by a batch process, all components of the polymerization mixture being initially charged in the reactor, or by a seim batch process, with one or more components being initially introduced and the remainder being metered in, or a continuous one Polymerization are carried out, wherein the components are added during the polymerization. The dosages may optionally be carried out separately (spatially and temporally).

The formulations of FRP composites for the BMC technique

(BuIk Molding Compound) are known in the art. A typical formulation for unsaturated polyester resin compositions for molding compositions for the BMC technique contains 60 to 70 parts by weight of unsaturated polyester resin (as a 50 to 75% solution in styrene), 30 to 40 parts by weight of low-profile additives (as a 30 to 50% solution in styrene) such as polyvinyl acetate or polymethyl methacrylate, 0.5 to 2 parts by weight of initiator such as t-butyl perbenzoate, 150 to 200 parts by weight of filler such as calcium carbonate, 25 to 30 wt. Parts of glass fiber, 0.5 to 3 parts by weight of mold release agents such as zinc stearate, and optionally other additives, such as pigments, flame retardant additives. The formulations contain no thickening agents Tel such as basic metal compounds, such as oxides or hydroxides of metals of the 1st to 3rd main group of the PSE.

In the use according to the invention, the low-profile

Additive, preferably based on polyvinyl acetate or polymethyl methacrylate, wholly or partly replaced by carboxyl-functional polyvinyl acetate. In general, the carbo- xylated polyvinyl acetate solid resin in an amount of 10 to 100 wt .-%, preferably 50 to 80 wt .-%, each based on the weight of low-profile additive in the recipe used. It is expedient to use this additive in a styrenic solution.

The following examples serve to further illustrate the invention:

The viscosities of solid resin solutions in styrene with and without filler for various solid resins were determined:

Copol:

Polyvinyl acetate solid resin with 5% by weight crotonic acid units and a weight-average molecular weight Mw = 67,500. Homol: Polyvinyl acetate solid resin having a weight-average molecular weight Mw = 69,000. Homo2:

Polyvinyl acetate solid resin with weight-average molecular weight Mw = 116600. Copo2:

Polyvinyl acetate solid resin containing 5% by weight crotonic acid units and having a weight average molecular weight M w = 116750. Copo 3: solid polyvinyl acetate resin containing 5% by weight crotonic acid units and having a weight average molecular weight Mw = 137,000.

In each case, a 40% strength by weight solution of the listed polymers in styrene was prepared, and the viscosity of the solvents was determined. each determined at 23 ° C with a Brookfield meter. The measurement results are given in the following table and in the following graph as V in ST (viscosity in styrene) in mPas.

200 parts by weight of the styrenic polymer solutions were subsequently mixed with 300 parts by weight of calcium carbonate (omyacarb 5GU) and the viscosity of the dispersions was determined in each case at 23 ° C. using a Brookfield measuring instrument. The measurement results are given in the following table and in the following graph as V in ST + F (viscosity in styrene with filler) in mPas.

The table or the graph shows that, when the filler is admixed with the homopolymers, an extreme increase in viscosity occurs, whereas in the case of copolymers of comparable molecular weight, the increase in viscosity in the case of filler additions is very moderate.

Copol Homol Homo2 Copo2 Copo3

V in ST [mPas] 1030 1230 2310 3090 3700

V in ST + F [mPas] 9850 67400 71200 19000 32200

Claims

Claims:

1. Use of carboxyl-functional polyvinyl acetate solid resins as an additive in formulations without thickening agent for the production of BMC molded parts.

2. Use according to claim 1, wherein carboxyl-functional polyvinyl acetate solid resins having comonomer units which are derived from monoethylenically unsaturated monocarboxylic or dicarboxylic acids are used.

3. Use according to claim 1 or 2, wherein the proportion of comonomer units having carboxyl groups in the solid polyvinyl acetate resin is 0.5 to 10 wt .-%, based on the total weight of the solid polyvinyl acetate resin.

4. Use according to claim 1 to 3, wherein the formulation 60 to 70 parts by weight of unsaturated polyester resin (as a 50 to 75% solution in styrene), 30 to 40 parts by weight Low-profile additives (than 30 bis 50% solution in styrene), 0.5 to 2 parts by weight of initiator, 150 to 200 parts by weight of filler, 25 to 30 parts by weight of glass fiber, 0.5 to 3 parts by weight of mold release agent, and optionally other additives.

5. Use according to claim 4, wherein 10 to 100 wt .-%, based on the weight amount of low-profile additive in the recipe, are replaced by the carboxyl-functional polyvinyl acetate solid resin.

6. Use according to claim 4, wherein 50 to 80 wt .-%, based on the weight amount of low-profile additive in the formulation, are replaced by the carboxyl-functional polyvinyl acetate solid resin.