DE4110219A1 - METHOD FOR PRODUCING PREPREGS WITH SOLVENT-FREE EPOXY RESIN - Google Patents

Abstract

Described is a process for the manufacture of resin-impregnated carrier sheets for laminates intended for electrical applications, in particular a process for the manufacture of prepregs. The epoxy-based thermosetting resin system is free of solvent. The accelerator and the catalyst are completely soluble in the epoxy resin. Proposed for use as the catalyst is a thermolatent catalyst with a starting temperature TS preferably lying above 115 DEG C. Proposed as accelerators are phenol novolaks. The resin system is particularly suitable for application using hot-melt techniques.

Description

Technical field

The invention relates to a method for producing synthetic resin impregnated carrier webs for electrical laminates, in particular for Production of prepregs according to the preamble of claim 1.

Prepregs are substrates impregnated with resin, in general Glass fiber webs, whereby the resin is not yet full constantly hardened (B-) state.

To a large extent, prepregs become so-called basic material boards (Circuit Boards) processed. Base material boards are copper-clad laminates on one or both sides made of in general NEN fiber-reinforced, thermosetting resins, which Resin is in the C state. They are used to make lei terplatten for the electronics industry and possibly for further processing to multilayers.

A common process for making copper-clad Base material boards is the pressing of several layers of Prepreg cuts with cover layers made of copper foil under application of pressure and heat, whereby the resin of the prepregs in the C- Condition is cured. The is of great importance Compliance with the narrow viscosity limits of the resin used under the pressing conditions, on the one hand a too strong out to prevent the resin from entering the edges and, on the other hand, to achieve a sufficient bond.

For the production of prepregs with epoxy resins on bisphenol-A- Base will be z. Currently almost exclusively solvent-based Approaches with dicyandiamide (dicy) used as hardener. The Resin mixtures usually contain a high proportion of tetrabromium bisphenol-A (TBBA) to achieve sufficient flame retardancy mung. Glass cloth almost exclusively serves as substrates nen.  

As a curing accelerator (catalyst) are usually tertiary amines such as B. benzyldimethylamine or imidazoles ver turns.

In these batches, solvent contents of 35-50% by weight necessary to ensure adequate penetration and wetting of the Glass fabric sheets and complete solubility of the hardness to reach (Dicy).

State of the art

For economic and ecological reasons Long efforts have been made to reduce solvents to use or -free resin approaches.

DE-A1 25 58 200 describes a generic method for continuous production of prepregs based on solvent-free, preferably thermosetting synthetic resins known in which the resin in solid, finely divided form sprinkled a textile backing and over the enamel point of the resin is heated. The melted resin pene Then trier into the carrier web, after which the resin immediately is cooled. The epoxy resin specified in this document however, contains neither a hardener nor a catalyst, so that it is not in this form for prepregs for electrical laminates can be used. Also common epoxy resin approaches for Electrolaminates with dicyandiamide as hardener can be used for this Process not used because of the hardener because of its lack of solubility not evenly due to the tissue sub strat penetrated. For this reason, the procedure according to the DE-A1 25 58 200 has not previously been used in industrial practice has been set.

From the company brochures "A new, improved performance, one component FR-4 epoxy resin, laminating system, printed circuit World Convention IV, Tokyo 1987 "," Research Product Technical Bulletin Shell Chemical Company, RSM-1212-BH-60, January 1987 " and EP-A2 02 11 382 are so-called one-component epos xid resin systems known that a dicyandiamide-free hardener  contain. The hardeners used here are complete soluble in the resin, yet these one-component Resins have a solvent content of approx. 25 wt Solution of the catalyst and adequate wetting and Penetration of the tissue substrate during prepreg production guarantee. As a curing accelerator (catalyst) at these one-component systems methylimidazole (MI) recommended.

From DE-A1 39 15 823 is a resin / hardener system for the manufacture development of composite materials in double belt presses known cure extremely quickly by adding large amounts of imidazoles tet. Due to the insolubility of the imidazole catalyst used tors, however, only arise at higher solvent contents satisfactory results.

task

The object of the present invention is to provide a method for Production of resin-impregnated carrier sheets for electrolami nate with low solvent (<5% by weight) or solvent free (<0.5% by weight) epoxy resin batches len, which is the production of prepregs with defined viscos would do under pressing conditions that ent those of conventional prepregs speak, enables.

Another concern of the invention is the manufacture of Epoxy based prepregs with substrates other than Glass fabrics, in particular with paper as the carrier material.

Presentation of the invention

The invention solves this problem by a method in which a thermosetting resin system based on epoxy resin with a solvent content of less than 5% by weight is brought into contact with the carrier web in solid or liquid form and in which the resin penetrates into the carrier web at elevated temperature, wherein the resin system contains an epoxy resin, a hardener and a thermolatent catalyst, and wherein the hardener and the catalyst are completely soluble in the epoxy resin at a temperature below the starting temperature T _{S of} the catalyst.

A low-solvent or preferably solvent-free resin with a hardener and catalyst dissolved therein is produced by mixing the components below - preferably 15-40 ° C. below - the starting temperature T _{S of} the thermolatent catalyst used. Thermolatent catalysts are known, for example, from DE-A1 34 47 241 (corresponds to EP-B1 01 91 926), where thermolatent catalysts are used in a very low viscosity epoxy resin batch with acid anhydride hardener. With regard to the properties and manufacture of the thermolatent catalysts, reference is made to these documents.

The starting temperature T _{S of} a thermolatent catalyst is the temperature at which the curing reaction of the resin begins "noticeably" for the first time. For the present invention, the starting temperature T _{S is} determined by a differential thermal analysis (differential scanning calorimetry, DSC analysis) as follows:
A sample (approx. 15 mg) of the resin / hardener / catalyst mixture used in accordance with the invention and, in parallel, a comparison sample (without catalyst) are carried out in a conventional automatic DSC apparatus (Mettler DSC TA 3000, DSC 20) with a heating rate of 5 ° C / min warmed. The difference between the performance of the sample and the comparison sample required for heating is measured. The exothermicity of the reaction can be determined on the basis of these measured values: If the difference in heating power is plotted against time / temperature, the area between the baseline and the curve corresponds to the enthalpy released during the curing reaction. The baseline compensates for measurement errors that z. B. by different Wäreka capacities arise before and after heating. The temperature at which the exothermic hardening reaction of the sample has elapsed is defined as the start temperature T _S.

A so-called one-component system can be used as a resin / hardener combination be used as it is from the company publication "Specifications Quatrex 5010, Dow Chemical Company", the  EP-A2 02 11 382 or the company publication "Research Product Technical Bulletin Shell Chemical Company, RSM-1212-BH-60, January 1987 ". These one-component systems include partially phenol novolaks as hardeners and do not contain any Dicyandiamide and no acid hydride hardener. Is preferred a resin / hardener combination according to DE-A1 39 15 823 used.

According to a preferred embodiment of the invention, 2-methylimidazole dibutyl phosphate (2-MI. DBP) is used as the thermolatent catalyst. This salt decomposes at a temperature of approx. 125 ° C in 2-methylimidazole, which then acts as a catalyst, and dibutylphosphoric acid, which is incorporated into the epoxy resin system. Below the decomposition temperature, 2-MI · DBP has practically no catalytic effect. This preferably used latent catalyst has a starting temperature, measured according to the DSC analysis, of 129 ° C. The thermolatent catalyst is dissolved in the resin / hardener system according to the invention preferably at 80-100 ° C., ie 25-45 ° C. below the starting temperature of the thermolatent catalyst. The starting temperature T _{S of} the thermolatent catalyst is preferably <115 ° C, in particular <120 ° C, and the temperature at which the thermolatent catalyst is dissolved in the resin / hardener system is preferably at least 10 ⁰ C lower.

In order to ensure good penetration of the carrier web, preferably a glass fabric web, the impregnation of the carrier web is preferably carried out at a temperature above the starting temperature T _S , in particular at about 130-150 ° C. within 0.5-2 min, in particular within 40-60 s. The web, which preferably has a resin content of 40-45% by weight, is then cooled to such an extent that a further reaction of the resin is stopped. In this phase, the hardened resin (B state) has a gelling time of approx. 100-130 s at 170 ° C; this corresponds to the values usual for multi-level presses.

A major advantage of the method according to the invention is that the mixing of the components, in particular the mixing of the catalyst into the resin / hardener system, at a relatively high temperature, ie 40 to 90 ° C. above the melt temperature of the resin, but below that Starting temperature T _{S of} the catalyst, preferably 10 to 50 ° C below T _S , takes place without the reaction being started noticeably. The metering of the resin batch necessary for impregnation is also preferably carried out at temperatures below the starting temperature T _{S of} the latent catalyst. To penetrate the carrier web, higher temperatures are preferably chosen, in particular a temperature of 5 to 40 ° C. above the starting temperature T _{S of} the thermolatent catalyst. The reaction is started at this temperature, so that the resin partially cures. The reaction in the B state can be stopped by rapid cooling of the impregnated web, so that a prepreg with an adjustable viscosity or glass transition temperature TG of the resin is obtained. This prepreg behaves under the pressing conditions in the production of the laminates, preferably in multi-day presses, exactly like a resin accelerated with a conventional catalyst, so that the pressing conditions need not be changed compared to the known pre-pregs.

Brief description of the drawing

The invention is illustrated below with the aid of an embodiment game and the drawing explained in more detail. It show

Fig. 1 schematically shows a hot melt system for impregnating the glass fabric carrier web

Fig. 2 is a DSC analysis with sales analysis to determine the T _S of 2-MI (comparative)

. Figure 3 is a DSC analysis with sales analysis to determine the T _S of 2-MI: DBP

Fig. 4 shows the temperature curve of the resin in the prepreg Her position (schematically)

example

A glass fabric 1 (US-Style 7628) with a surface weight of 200 g / m ² is coated with a commercially available hot-melt system according to FIG. 1 as follows: A solvent-free epoxy resin with a novolak based on a bisphenol (type VE 4107 or VE 3916 "solvent-free", from Bakelite), into which 0.5% by weight of 2-methylimidazole dibutyl phosphate (2MZ · DBP) were dissolved at 90 ° C. The resin 4 is heated to a temperature of 65 ° C. and pumped into the gap between the doctor blade 5 and the roller 6 . As a result, a uniform liquid resin film 7 on the release paper 3 chen chen. The liquid resin film 7 is brought into contact with the carrier fabric 1 in the region 2 and heated evenly by the heating device 8 . The heating power is controlled so that the resin has a max. Temperature of approx. 140 ° C reached. At this temperature, excellent wetting of the fabric is achieved on the one hand due to the initially very low viscosity of the resin, and on the other hand the curing reaction is started very quickly by the disintegration of the latent catalyst, so that the desired B state of the resin 4 is reached after a short time. By a suitable choice of the length of the heating device 8 or the throughput speed of the web 9 , a dwell time of the web in the temperature range between 130 and 140 ° C. of approximately 60 S is set. Following the heater 8 , the web is z. B. cooled with cooling air and thus the white direct reaction of the resin stopped.

In Fig. 3 the determination of the starting temperature T _{S of} the thermolatent catalyst 2-MI · DBP is shown:
15 mg each of the solvent-free VE 4107 resin were analyzed in a "Mettler TA 3000" type DSC device. 0.5% by weight of 2-MI · DBP was dissolved in one sample and the other sample contained no catalyst. The two samples were heated simultaneously at a heating rate of 5 ° C./min, the difference between the heating powers ΔP required for this being determined as a function of the time or the temperature T. In the left view of FIG. 3, this heating power difference AP as a function of the temperature T (curve 10). Due to the baseline (curve 12 ), which is automatically calculated by the system (setting at Mettler: baseline type 8), measurement errors are e.g. B. compensated by temperature-related differences in heat capacity of the samples, etc. The area between curves 10 and 11 is a measure of the enthalpy released during the hardening reaction. The course of the reaction can be determined automatically from these values (curve 12 , right representation in FIG. 3). From this figure it can be seen that the reaction of the resin with 2-MI · DBP begins at about 120 °. The starting temperature, at which the reaction has run to 2%, is 129 ° C.

In comparison to this, the course of the curing reaction of the same resin with 0.1% by weight of 2-methylimidazole is shown in FIG. 2: Here the reaction already begins at approx. 80 ° C. while the starting temperature (2% conversion ) is approx. 100 ° C. The pot life of such a resin approach would be too short for a hot melt process.

In both cases the max. Reactivity (maxima of the functions curves 10 and 13 ) reached at approx. 168 ° C. This ensures that the resins behave identically under the pressing conditions.

In FIG. 4, the temperature curve of the resin is shown in the present example, during the mixing (90 ° C) and dosing (65 ° C) take place substantially below the starting temperature T _s, the temperature during impregnation of the fabric substrate with about 140 ° C above T _S. The prepregs are stored at room temperature.

A major advantage of the method according to the invention lies in that prepregs are made with solvent-free resins can be, in which the resin under pressing conditions in Multi-day presses show the same viscosity curve as usual FR-4 resins. Another advantage of the invention The process is that paper webs are also used as substrates can be set, while usual resin approaches with dicyan diamid as hardener cannot be processed with paper substrates can.

Claims (5)

1. A method for producing synthetic resin-impregnated carrier webs for electrolaminates, in particular for the production of pre-pregs, in which a thermosetting resin system based on epoxy resin with a solvent content of less than 5% by weight in solid or liquid form is brought into contact with the carrier web and in which Resin penetrated into the carrier web at elevated temperature, characterized in that the resin system contains an epoxy resin, a hardener and a thermolatent catalyst and that the hardener and the catalyst are completely soluble in the epoxy resin at a temperature below the starting temperature T _{S of} the catalyst . 2. The method according to claim 1, characterized by the use of a thermolatent Ver with a starting temperature T _S above 115 ° C, preferably above 120 ° C. 3. The method according to any one of claims 1 or 2, characterized net by using phenol novolaks as hardeners. 4. The method according to any one of claims 1 to 3, characterized in that the catalyst is dissolved in the resin / hardener mixture at a temperature which is at least 10 ° C below the starting temperature T _{S of} the catalyst that the penetration of the carrier web a temperature above the start temperature T _S and that the resin-impregnated carrier web is then cooled to fix the resin in the B-state. 5. The method according to any one of claims 1 to 5, characterized through the use of paper webs as carrier webs.