JPS6038408B2 - Method for producing sheet-like and bulk-form molding materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing sheet or bulk molding materials, and more particularly to a novel accelerator comprising a specific chemical thickener and a cobalt (m) accelerator. By using the composition, the molding composition can be stored in sheet or bulk form for a long period of time at a temperature lower than the molding temperature, but once the molding temperature is reached, the reactivity is sufficiently increased. The present invention relates to a method that increases the curing speed and enables rapid curing.

The present invention will be explained in detail below. The use of unsaturated polyesters as molding materials is already known and has been widely used industrially for several decades.

However, the origins of sheet molding materials (SMC) and bulk molding materials (BMC) consisting of unsaturated polyester resins and vinyl monomers have only recently begun. It is now possible to mix and prepare molding compositions in large quantities and store them in sheet or bulk form for later use. (Before this was developed, non-stick materials were difficult to obtain and molding processes containing large amounts of resin were unavoidable.) This occurs when using a material that has been used in the past, and in this case, the polyester resin separates from the glass.) When manufacturing a sheet or bulk molding material, chemical thickening thickne
r), a curing accelerator, a catalyst, a reinforcing agent, a filler, and a mold release agent (1) are mixed with an unsaturated polyester resin component and an unsaturated or vinyl monomer component to form a sheet; Then wind it onto a reel or
After mixing the above ingredients, it is formed into a pellet or sausage-like bulk.

In the production of SMC and BMC, the development of the following promoters and catalysts is a technical challenge.

In other words, these promoters and catalysts can be easily mixed and added to the molding composition during the preparation of the molding composition, and remain substantially inactive at temperatures lower than the molding temperature. However, when the molding temperature is reached, it is sufficiently activated to catalyze or catalyze the crosslinking and curing process of the molding composition. The development of promoters and catalysts that have such properties has become a technical challenge.
To cure (cme) unsaturated polyester resin,
Although there are many so-called catalysts or accelerators, these are highly reactive and will gel before molding, making them unsuitable for producing sheet or bulk molding materials. . A number of patents disclose the use of organometallics to accelerate the cure rate of unsaturated polyester resins.

Typical organometallics include soluble salts of reactive metals, such as: manganese caprylate, cobalt naphthenate, cobalt caprate.
ecanoate), lithium cabrylate, lithium thiocyanate, aluminum laurate, aluminum octoate (ratio ate), and gallium octoate. However, since these salts have too high reactivity, only SMC and BMC with low shelf life are obtained. In order to cure unsaturated polyester resins, it has been proposed to use organometallic and cobalt salts of the type described above in combination with pereste, peroxides, and hydroperoxides. has been done.

Examples of peroxides, beresters, and hydroperoxides suitable for use with cobalt salts include methyl ethyl ketone peroxide, te-butyl perbenzoate, te-butyl perlaurate, and the like. 2
・Enolizable ketones such as 4-pentanedione,
Organometallic or cobalt salts of 8-diketones have also been used to accelerate the curing of unsaturated polyester resins.

For example, cobalt acetylacetonate has also been found to increase the cure rate of unsaturated polyester resins. In order to facilitate curing of unsaturated polyester resins, cobalt salts are used in combination with chelating agents such as ethylenediaminetetraacetic acid and, if necessary, peroxide catalysts or triethylenediamine. There is.

Generally, organometallic accelerators used in the production of polyester resins are not suitable for initiating polymerization curing of SMC or BMC.

The reason is that these accelerators have a poor shelf life. If the storage temperature is 750F, gelation may occur within a few days or less. For this reason, high temperature peroxide and hydroperoxide catalysts are initially used to catalyze the reaction, and organometallics are excluded from their use. The present invention is characterized by the use of a novel accelerator composition, and the method of the present invention is effective for increasing the shelf life of a molding material consisting of an unsaturated polyester resin and an unsaturated monomer. and the accelerator composition is soluble in and copolymerizable with the molding material at a temperature lower than the molding temperature, but when the single molding temperature is reached, ,
It has sufficient reactivity and increases the curing speed.
This is what was discovered.

In addition, the accelerator
When the composition is used in conjunction with said molding composition consisting of an unsaturated polyester resin and an unsaturated monomer, the aforementioned sheet and bulk molding compositions can be successfully produced by chemical thickening treatment. The accelerator composition used in the present invention comprises a cobalt-containing accelerator and a coupler; the nuclear cobalt accelerator is a cobalt halide containing 2 carbon atoms
cobalt salts of monocarboxylic acids having a carbon acetate of from It is used in the range of 1 to 450 based on the metal cobalt (blood), and is selected from the group consisting of calcium and magnesium oxides and hydroxides. The accelerator composition used in the present invention has the following advantages: sheet and bulk molding materials with a long shelf life of 18-20 days even under accelerated test conditions of 1000F; can be manufactured.

In contrast, with the prior art it is only possible to produce sheet and bulk molding materials with a shelf life of only 3 to 13 days; Sheet and bulk molding materials can be produced so that gelling of the resin when placed in a mold is minimized; It is possible to produce a molding material that does not discolor badly.

In order to produce a sheet-like molding material or a bulk-like molding material according to the present invention, it is necessary to synthesize a thermosetting polyester resin. and at least one polyhydric alcohol.

Typical polycarboxylic acids include maleic acid, fumaric acid, mesaconic acid, citraconic acid, and glutaconic acid. If necessary, add saturated polycarboxylic acid to 4
It may be used in combination up to 0%. These saturated polycarboxylic acids include (iso and ortho) phthalic acid, succinic acid, adipic acid, and sebacic acid. Typical polyhydric alcohols include glycols such as diethylene glycol, trimethylene glycol, propylene glycol, and ethylene glycol, as well as trimethylolpropane and alkoxylated products thereof. In order to effect cross-linking with the unsaturated polyester component, the unsaturated monomer is bonded to the unsaturated polyester resin to form a thermosetting polyester resin.

The curing process is accomplished by a copolymerization reaction between the unsaturated monomer and the unsaturated polyester resin, so that the resin changes from a liquid to a solid and becomes substantially cross-linked and insoluble. It becomes gender. The unsaturated monomer capable of forming cross-linkages when reacted with the unsaturated polyester resin must be capable of substantially dissolving in the unsaturated polyester resin to form a uniform dispersion. Unsaturated monomers suitable for cross-linking with thermosetting polyester resins include, for example, vinyl monomers such as styrene, butadiene, methylstyrene,
Methyl methacrylate, ethyl acrylate, vinyl acetate,
and allyl monomers such as allyl acetate and allyl alcohol. A chemical thickener is added to the thermosetting polyester resin containing the unsaturated monomer in order to thicken the resin composition to facilitate subsequent operations.

As mentioned above, it is already known to use chemical thickeners to increase the viscosity of unsaturated polyester resins and unsaturated monomers. Generally, oxides of metals from group 0 of the periodic table and their hydroxides are used as thickeners. Particularly effective are magnesium oxide, magnesium hydroxide, and calcium oxide, calcium hydroxide, although barium oxide, barium hydroxide, and zinc oxide may also be used in the practice of this invention. For reasons of efficiency and economy, mention may be made of the oxides or hydroxides of magnesium and calcium as suitable chemical thickeners. These compounds are
They may be used alone or in combination with each other. The amount of these thickeners used is appropriate, that is, 0.5 to 25 parts per 10 parts of the resin, but usually,
The amount is 1 to 5 parts per 10 bales of resin. Cobalt (m)
It is clear that the system curing accelerator reacts synergistically with the chemical thickener.

That is, moderately low temperatures, i.e., room temperature to 1000F, will increase shelf life, but a molding temperature of about 3000F will provide sufficient reactivity to provide the desired exothermic temperature for take-up and hardness. This accelerates the G rate. Cobalt promoters suitable for use in the present invention are those in which the cobalt ion exhibits an m-valent state. Examples of cobalt promoters suitable for carrying out the invention are: cobalt salts of monocarboxylic acids having 2 to 20 carbon atoms (sometimes this is referred to as cobalt soap), e.g. Cobalt, cobalt(II) caprate (c
cobaltic neodecanoa
), cobalticocacrylate (cobalticoc
cobalt naphthenate (m); 8-
Cobalt salts of diketones, such as cobalt (m) acetylacetonate
toMte) and cobalt(m) acetonyl acetonate (cobalticace nylacebnate)
): and inorganic cobalt salts having dispersibility, such as cobalt(II) fluoride, cobalt(II) hydroxide, cobalt(II) oxide, cobalt(II) chloride, cobalt(II) sulfate, and others.

Suitable cobalt promoters are organic or inorganic promoters that have the property of being highly soluble in polyester resins. Due to its high solubility, this accelerator is dispersed uniformly throughout the molding material and pre-gelled (pre-gelled) prior to the molding process.
This can reduce the possibility of localization of areas that may undergo pre-gel and localization of cold spots. The cobalt accelerator must be added, necessarily in the trivalent state, to the polyester resin and the unsaturated monomer and thoroughly mixed therein prior to the production of the sheet or bulk molding material.

In the practice of the present invention, at least an effective amount of a cobalt (rainbow) accelerator is used to selectively extend the shelf life of the molding composition and selectively increase the cure rate.
Add r) to ticpromo. The amount added is usually 100% of the unsaturated monomer-containing polyester resin (
0.006 to 0.03 parts by weight of cobalt metal
It is 6 parts (by weight). 0.0075 parts of metallic cobalt per 10 parts of unsaturated monomer-containing polyester resin
Preferably, ~0.03 part is used. Metallic cobalt (m
If less than about 0.006 parts of ) are used, shelf life is somewhat reduced. Similarly, if more leather uses cobalt metal, the cure rate will decrease slightly.
Good results can be obtained within the above range, but
Particularly good results are obtained when about 0.01 to 0.03 parts of metallic cobalt are used per 10 parts of polyester resin. If the amount of metallic cobalt used is more than 0.036 parts, the storage stability of the molding material will be lowered and the reaction initiation temperature will be lower, resulting in some gelation before molding. be. In addition, the fact is that cobalt (m)
Higher salt levels will also slow down the curing rate of the polyester at molding temperatures, thereby reducing its efficiency. Also, increasing the amount of cobalt promoter used can increase the overall cost of the molding material without providing any significant benefit. A combination of a cobalt accelerator and a chemical thickener is an accelerator (
This accelerator composition exhibits a synergistic effect that was not observed when each of these components was used alone.

The effect is not simply additive with the expected values of each addition of a thickener, ie, coupler, and accelerator to the molding composition. For example, even if a cobalt accelerator is added to the raw molding material in the absence of a thickening agent or a coupler, its shelf life will be lower than when the accelerator is used in combination with a thickener, i.e., a coupler. do. Similarly, the use of thickeners or couplers alone, with the exception of cobalt accelerators, also reduces shelf life and, of course, in the absence of accelerators, cure rates are substantially reduced. Resulting in. Obviously, at temperatures below the molding temperature, such as from room temperature to about 1000F, the thickener or coupler has the property of deactivating the cobalt(m)-based promoter; However, if the temperature is the molding temperature or the desired maximum exothermic temperature (exothe skin
At temperatures slightly below the perature, the thickener or cobbler releases the cobalt accelerator from its inactive state and activates it, speeding up the curing rate of the polyester resin. This accelerator composition is
The components may be added singly or both components may be added at once during the manufacturing process of the molding material, as long as they are mixed substantially uniformly.

For example, before manufacturing the molding material, the accelerator composition may be prepared in advance and added to the molding material, or each component may be added separately. In some cases it may be preferable to disperse the accelerator composition in a carrier and to add this dispersion to the molding material. The thickener or coupler is composed of an oxide or hydroxide of calcium or magnesium, and the proportion of the thickener or coupler added to the accelerator composition is as follows:
Approximately 1 for the metallic cobalt present in the cobalt promoter
~450 parts by weight. Preferably, this ratio is about 30 to 60 parts, but a more preferred ratio is about 50 to 40 parts of coupler to cobalt metal. When the proportion of the thickener or coupler is less than about 1 part of the cobalt metal present in the accelerator, the accelerator composition is dissolved in a polyester resin syrup consisting of an unsaturated polyester resin and a vinyl monomer. Even if added, adequate coupling or thickening properties cannot be obtained. On the other hand, if the ratio of thickener or coupler exceeds about 450 parts of anchor relative to the cobalt metal present in the promoter, then the thickener or coupler should be added in an amount greater than or equal to the thickening required. will exist. More importantly,
In the above cases, the amount of cobalt accelerator is generally insufficient, and the curing speed does not increase even when the molding temperature is reached, and the shelf life of the molding material does not improve. It is. It is more effective when the ratio of thickener or coupler to cobalt metal is 30 to 60 parts of thickener or coupler to cobalt promoter, preferably 50 to 40 parts of cobalt metal. A good product is obtained and economic objectives are also achieved. In general, when catalyzing the curing of polyester, 0.2
Berester, a peroxide or hydroperoxide catalyst, is used in a proportion of 5 to 2 parts by weight; the use of Berester in combination with a cobalt catalyst further increases the curing rate. However, this catalyst must be selected and used with great care. The reason is that some of these catalysts
This is because it has a property of shortening the shelf life (shelf ship) of SMC or BMC because it has lower stability and higher reactivity than others. For example, when methyl ethyl ketone peroxide and cobalt acetylacetonate are used together, the shelf life is lower than when the more stable cumene hydroperoxide is used in combination with a cobalt promoter. be. However, when compared to molding materials without organometallic promoters or other types of organometallic promoters, the shelf life of molding materials containing each component is reduced when cobalt ion is present. , it certainly extends. Examples of verester, peroxide and hydroperoxy catalysts that can be used in the practice of this invention are: t-butyl perpenzoate, t-butyl peroctoate.
perocbate), 2,5-dimethyl-2,5-bis(2-ethylhexanoylberoxy)-hexane, cumene hydro/gu-oxide, diisopropyl hydroperoxide, 1,1,113,3-tetramethylbutylhydroper oxide, and methyl ethyl ketone/gu oxide.

As is well known, when producing SMC and BMC, various ingredients can be added to achieve the desired effect.

When producing alkyd-type sheet and bulk molding materials, a drying oil may be added to the polyester composition. Examples of drying oils suitable for this application include:
Oishtica oil, tung oil, linseed oil, soybean oil, and castor oil may be mentioned. In order to achieve the desired purpose,
The following can also be used: fillers such as, for example, calcium carbonate, clay, asbestos, and aluminum hydride; scale agents, such as, for example, zinc stearate, calcium stearate, polyethylene; and, for example, titanium dioxide, ferric oxide, litharge, zinc oxide,
pigments such as zinc sulfide, and others. The use of said molding compositions in the production of reinforced polyesters is often advantageous, but this operation typically requires approximately 1/4
This can be achieved by incorporating glass fibers of ~2" length into the molding material. Recently, in order to prevent shrinkage phenomena during the molding process, low shrinkage components or low profile ) It has become common practice to add ingredients.

Without the addition of low-shrinkage or low-profile components, it is difficult to obtain very precise molded parts, and the surfaces may form corrugations or ribs. Typically, this low-shrinkage or low-profile component is a thermoplastic resin dissolved in vinyl monomer (
This low shrinkage component is leached from the mixture of polyester resin and vinyl monomer as a discontinuous phase during cure and molding.
This fills the voids left by the shrinkage of the polyester resin. Typical low shrinkage additives include:
Examples include polyacrylates such as polymethyl methacrylate, thermoplastic resins such as polyvinyl chloride, polyethylene, and polyvinyl acetate. Anything that is commonly used in practice for producing low shrinkage or low profile resins can be used here as well. The reference examples and examples described below are provided to explain the present invention in more detail, and are not intended to limit the scope of the present invention.

All parts and percentages herein are by weight unless otherwise specified. Reference Examples Typical compositions used to produce bulk and sheet molding materials are as follows: These materials are thoroughly mixed in a high-power kneader or thoroughly homogenized. decentralize it.

The mixture thus obtained, i.e., the premix, is aged for several days and then cut into pieces of appropriate size.
It is molded and cured within a temperature range of 250F for a short period of time, e.g., 1 to 3 minutes. Except for changing the type of metal promoter used to promote the reaction.
Other resins are manufactured according to the resin manufacturing method described above,
The performance characteristics of the resin were measured.

In this case, fillers, thickeners, thickeners, and glass reinforcements were omitted from the pure resin. Tests performed to determine performance characteristics were gel time, cmerate, reaction onset temperature, and peak exotherm test; these measurements were performed using SPI for drawing exotherm curves. It was carried out by standard block test method using method. This standard block test method (BI Test Meth) is disclosed at: 24th Annual Technical Conference (
Annual Technical Conference
), 196 King's IJ Print; Reinforced Plastics/Co
The SMiety of Plastics
dfemale thi). Take 300 ta of each composition (paste) from which the glass fibers have been removed, put it into a can with a lid immediately after mixing, store it at 1000F, and measure the storage stability under accelerated conditions. did.

The contents of each can were checked daily by inserting a screwdriver and measuring its permeability. When the tip of the screwdriver blade could no longer reach the bottom of the can, it was considered that the paste could no longer be shaped on the press, and the shelf life of the paste ended here.
The resins used to formulate the molding compositions were Paraplex P-340 and Paraplex 701.

Paraplex P-340 is a styrene solution of a highly reactive polyester, but this polyester contains glycols (0.7 moles per 7.3 moles of propylene glycol).
mole of ethylene glycol) and cis and trans butenedioic acid
(usually referred to as fumaric acid and maleic acid), and the proportion of polyester in Paraplex P Ichihiro 0 is 65 to 7 parts by weight, and the proportion of styrene is 35 to 3 parts by weight. It is. Paraplex 701 is a low shrinkage component made of thermoplastic acrylic resin dissolved in styrene. Paraplex P-10 and Paraplex P-701 are manufactured by Rohm and Haas
hmanddayaasCo. ), and is also a trademark of P-
A mixture of P-340 and P-701 is commercially available as Paraplex P-1 blood. The ratios of resin components, catalysts, and cobalt curing accelerators, as well as gel time, maximum exothermic temperature, and reaction initiation (kickoff) temperature are listed in Table 1 below. Table 1 SPI Pullock exotherm data (at 300F) 0o+3 Effect of acetylacetonate and other metal promoters on gel time, cure time, maximum exotherm, and reaction initiation temperature1 2 3 4 5 6 7 8 9101
1 Paraplex P-340
60 60 60 60 60 60
60 60 60 60 60 Paraple
x P-701 40 40
40 40 40 40 40 40
40 40 40T-butyl barbenzoate
1 1 1 1
1 1 10o 012.6th 20
×Cobalt naphthenate dish
*
*Triethylene diamine and ○o○
1-2/6 days 20 Kikobalt dish acetylacetonate
× ★Cobalt dish acetylacetonate
Concubine *Acetylacetone

03.
03 Gluing time (minutes)
13 1.1 0.1 02 0.6 0.2 0.4
1 10 4 0.2 Curing time (min)
21 1.4 0.4 0.5 09
05 0.7 1.3 15 5 0.4 Maximum fever
(r) 405 443 427 4
62 445 458 478462 355 347
400 Reaction initiation temperature (F) 315
230 90 170 235150 225 22
5 310 305 145 Astringency Addition of active metal by 0.012 From the results shown in Table 1, the following can be seen.

That is, when purely polyester resin is used, the curing time of the resin promoted with cobalt and catalyzed with t-butyl perpenzoate (Sample 7) is longer than that of the resin that is not accelerated (Sample 2). is almost 1/
2, but on the other hand, the reaction initiation temperature to prevent pre-gelation within the mold is approximately the same.
Although the use of other organic accelerators, as in the case of samples 3, 4, and 6, has the effect of increasing the curing rate, due to the low reaction initiation temperature, the resin It will turn into a gel when you put it in the mold. Furthermore, the following can be seen from the results in Table 1.

That is, in the case of sample 10, its curing time (cmeti
As can be seen from the fact that me) is about 1/4 of that in sample 1, cobalt ions are effective in accelerating curing in systems that do not use catalysts, and this is due to the accelerated treatment with acetylacetone. This resin is even more effective than the resin that was used (see sample 8). Examples Compositions suitable for producing sheet-like and bulk-like molding materials were produced according to the same method as in Reference Examples, except that the formulation was changed to the compositions shown in Table □ below.

These compositions were tested for shelf life at 1000F, which corresponds to a shelf life test under more accelerated conditions compared to normal shelf life tests conducted at 750F. And for some of these compositions, a 1/4" to 1/8" down pressure mold is used.
) was tested for cure data at 3000F. Table 1-1 Effect of combined use of cobalt plate acetylacetonate and Group 11 metal base oxide on aging acceleration of SMO paste and shelf life of paste 1
2 3 4 5 6 7 8 9 10Par
aplex P-340 60 60
60 60 60 60 60 60 60 60
Paraplex P-701 40
40 40 40 40 40 40 40 40
40t-butylpa-1'-kunzoate
1 1 1 1 1
1 1 1 1 10o012.6
Day 20 *Cobalt naphthenate QO
*Triethylenediamine and ○o012・6th 20
*Cobalt 00 acetylacetonate
Togicobalt Dish Acetylacetonate
zo × Chiacetylacetone
0.3 Zinc stearate
5 5 5 5 5
5 5 5 5 5○a003
150 150 1
50 150 150 150 150 150
150 150Mg■mark 2
2.5 2.5 25 2.5 2-5
25 2.5Mg0
1
．． 251/4″~1/8″ gradual pressure mold (at 300T
) Curing data obtained from "Gikisai/"・Curing time (minutes)
1.75 1.25
1.25 hardening treatment (minutes)
125 1.00 1.00 Barcol hardness 56 57
Storage stability of 56SMO paste at 1100T 10
-131-2 1-2 3-5 2-318-20 1
-2 2 26 >3>6 (Time until solidification...
...Unit is day): x Amount of metal added: 0.012 parts*
*10 more 1/4″ chopped strand glass fibers
Contains 8 parts by weight.

The following can be seen from the results in Table 0. That is, sample 6
and 9, the curing time and hardness of the cobalt(m)-accelerated SMC paste were compared to those of the cobalt(0)-accelerated resin (sample 2).
and 4) preferred. On the other hand, regarding the storage stability of SMC paste, pastes (samples 6 and 9) that were accelerated with primary cobalt promoter and thickened with Mg○ and Mg(OH)2 were compared with those that were accelerated with cobalt (m). Resin treated with but not increased occupancy treatment (Sample 8), Resin promoted with cobaltous cobalt (Samples 2, 3, 4, 5), and Resin promoted with cobaltous cobalt acetylacetone (Sample 8). When compared with sample 7), there is an incredible difference in preservation between them.

Although sample 4 appears to be equivalent to the cobalt (m) promoted resin in the reference example, it is certain that they are not equivalent in terms of shelf life.

Claims (1)

[Scope of Claims] 1. A chemical thickener consisting of a group II metal oxide or hydroxide and a cobalt (III) promoter soluble in the molding material for sheet-like and bulk-form molding materials. A method for producing sheet-like and bulk-form molding materials, comprising mixing at least effective proportions of and. 2. The method according to claim 1, wherein the molding material comprises an unsaturated polyester resin and an unsaturated monomer that is soluble therein and copolymerizable therewith. 3. Claim 1, characterized in that the thickener and the cobalt accelerator are added and mixed into the molding material at the same time.
The method described in section. 4. The method according to claim 1, characterized in that the thickener and the cobalt accelerator are added and mixed separately to the molding material. 5. The method according to claim 2, characterized in that the molding material contains a catalyst. 6. The method of claim 5, wherein the catalyst is selected from the group consisting of pelleters, peroxides, and hydroperoxides. 7. Claim 6, characterized in that the catalyst is contained in the molding material in a ratio of about 0.25 to 2 parts by weight based on the unsaturated polyester resin and the unsaturated monomer. Method described. 8. Adding and mixing the cobalt (III) catalyst to the molding material at a ratio such that metallic cobalt is 0.006 to 0.036 parts to 100 parts of the unsaturated polyester resin and unsaturated monomer. The method according to claim 7. 9. Claim No. 9, characterized in that the chemical thickener is contained in the molding material in a ratio of 0.5 to 25 parts per 100 parts of the unsaturated polyester resin and the unsaturated monomer. The method described in Section 8. 10 The cobalt (III) promoter is a cobalt (III) halide, a cobalt (III) salt of a monocarboxylic acid having 2 to 20 carbon atoms in its structure, cobalt (III) sulfate, and a cobalt (III) β-diketone. Claim 7, characterized in that:
The method described in section. 11 The cobalt (III) β-diketone is cobalt (
11. The method according to claim 10, characterized in that it is selected from the group consisting of III) acetylacetonate and cobalt(III) acetonylacetonate. 12. The method of claim 11, wherein the chemical thickener is a magnesium compound selected from the group consisting of magnesium oxide and magnesium hydroxide. 13. A method according to claim 12, characterized in that the molding material includes a thermoplastic polymer suitable for imparting low shrinkage properties to the molding material. 14. The method of claim 13, wherein the curing accelerator is cobalt (III) acetylacetonate and the catalyst is t-butyl perbenzoate.