DE3838717A1 - FORMING METHOD FOR HARD FORM PARTS - Google Patents

Abstract

A forming process for producing a hard shaped molded article comprising the steps of (a) providing a moldable thermosetting composition comprising a polybutadiene or polyisoprene liquid resin having a molecular weight less than 5,000 and at least 50% by weight 1,2 addition; and a thermoplastic elastomer comprising a first block copolymer having the formula Xm(YX)n or &lparstr& <Y>X &rparstr& n where Y is a polybutadiene or polyisoprene block having less than 50% by weight 1,2 addition, X is a thermoplastic block, and m and n represent the average block numbers in said copolymer, m being 0 or 1 and n being at least 1; (b) forming said composition into a shape, said thermoplastic elastomer enabling said composition to maintain said shape during said forming process, said liquid resin enabling the viscosity of said composition to be sufficiently low that said shape is readily formed; and (c) curing said composition to produce said article including subjecting said composition to a high temperature cure condition at a temperature greater than about 250 DEG C and less than the decomposition temperature of said composition. The composition used in the process can also include one or more dielectric fillers. The invention includes articles produced by this process.

Description

The invention relates to molding processes for hard moldings.

Thermosets are materials that are initially malleable, but covalently crosslink under the influence of heat or radiation, so as to form a three-dimensional network form that is not fusible and insoluble.

Thermoplastics, on the other hand, melt and remain molten (instead of crosslinking) Upon exposure to heat, so that they can be used in a variety of forms at higher temperatures can be processed.

Thermoplastic elastomers are block copolymers with thermoplastic blocks, as physical cross connections for the material at ambient temperature serve, but flow when heated, so that the material is moldable as a thermoplastic.

The teaching of the invention is given by the claims.

In particular, it has been recognized that hard, molded parts can be produced by Application of high-temperature curing above about 250 ° C, but below the Decomposition temperature of the thermoset composition, especially with the composition according to claim 3.

The first and second block copolymers are each a linear block copolymer (first formula) or a graft copolymer (second formula).

Claim 5: The filler is preferably dielectric, d. H. with dielectric constant about 1.2 at microwave frequencies, and so homogeneously dispersed in the composition, that after curing of the composition the properties the cured molding, z. B. Dielectric constant and coefficient of thermal expansion, at most about 5% fluctuate within the molding.

Claim 8: The crosslinking agent may co-cure, i. H. covalent bonds, effect with the resin and / or the thermoplastic elastomer.

Claims 10, 11: m = n = 1 and p = q = 1, respectively, wherein the ethylene-propylene block is the hydrogenated form of an isoprene block.

In the production of the moldings is a hardener (preferably a peroxide) for Acceleration of curing.

The compositions of the invention can be easily molded into a variety of different types Moldings with favorable isotropic thermal and dielectric properties. These properties can be chosen to reach or These include ceramics, especially gallium arsenide, alumina and silica / silica. Therefore, the cured moldings ceramic in many replace electronic and microwave applications, eg. B. as special substrates for fast digital and microwave circuits. Examples of microwave circuits In particular, microstrip circuits, microstrip antennas and Stripline circuits. The cured moldings can also be used as Rod antennas and chip carriers.  

The compositions have certain processing advantages.

First, they are easy to process, since the polybutadiene or polyisoprene resin is the Viscosity of the composition keeps easily manageable value. Size and shape The molded parts to be produced are limited only by the mold used. The processing is also economical, especially in comparison to processing of ceramics. The proportion of thermoplastic elastomer in the composition prevents the dielectric filler from separating from the resin during processing, so that "filler-rich" and "filler-poor" areas are avoided. Therefore, the thermal and dielectric properties of the cured molding substantially homogeneous throughout the molding. The thermoplastic elastomer reduces also the risk that the composition during the molding process steps Cracks forms.

The cured moldings are very resistant to environmental influences, eg. B. Water, higher temperatures, acids, alkalis and higher pressure. Therefore, the Compositions suitable as resins for capsulating articles, the like Be exposed to influences. In addition, if the cured composition with to connect a metal, for. B. on a circuit board, the thermal expansion coefficient corresponds the hardened thermosets of many metals. Therefore, a Loosen the bond during thermal cycling due to different Thermal expansion of the metal substrate prevents, cf. also claim 6.

The invention will be explained in more detail with reference to the following examples.

Structure and manufacture

The moldable thermoset compositions according to the invention have a Proportion of polybutadiene or polyisoprene resin (molecular weight below about 5000, preferably 1000 to 3000) and a proportion of thermoplastic elastomer. The resin- Proportion, which is a liquid at room temperature, maintains the viscosity of the Composition on easy to handle value during processing to this to facilitate. He also crosslinks during curing. Polybutadiene and polyisoprene resins with at least 90 wt .-% 1,2-addition are preferred because they show the highest crosslink density after curing because of the large number of hanging Vinyl groups available for crosslinking. High crosslinking densities are desirable because the products show better high temperature properties. On preferred resin is B3000 resin, a low molecular weight polybutadiene liquid resin having more than 90% by weight of 1,2-addition (available from Nippon Soda, Ltd.).

The proportion of thermoplastic elastomer maintains the shape in which the composition is molded while molding. He also prevents the filler at one Separation of the resin and reduces the cracking during molding. Further He participates in curing during curing.

As already mentioned, the proportion of thermoplastic elastomer has a linear or graft copolymer with preferably a polybutadiene or polyisoprene block having at least 90 wt .-% 1,2-addition and a thermoplastic block, preferably styrene or α- methyl-styrene is. The high level of 1,2-addition in the polyisoprene or polybutadiene block results in high crosslink densities after cure, as is the case with the polybutadiene or polyisoprene resin, as described above. A preferred copolymer is a styrene-butadiene-styrene triblock copolymer, e.g. Kraton DX1300 (available from Shell Chemical Corp.).

The thermoplastic elastomer may also have a second block copolymer which the first is similar except for the difference that the polybutadiene or polyisoprene block is hydrogenated to a polyethylene block (polybutadiene) or a Ethylene-propylene copolymer (in polyisoprene). When used together with the first Copolymer can be materials with particularly low coefficients of thermal expansion getting produced. This second block copolymer is preferably Kraton GX1855 (available from Shell Chemical Corp.) containing a mixture of styrene-high-1,2-butadiene-styrene block copolymer and styrene (ethylene-propylene) -styrene block copolymer should be.

A crosslinking agent having the functionality of at least 2 becomes the thermoset composition added to increase the crosslink density after curing. Examples of preferred crosslinking agents are triallyl cyanurate, diallyl phthalate, Divinyl benzene and polyfunctional acrylate monomers (eg, Sartomer resins, available by Arco Specialty Chemicals Co.), all of which are available.

Particularly preferred fillers are rutile titanium dioxide and amorphous silicas / Silica, since these fillers have high or low dielectric constant, so that a large dielectric constant range combined with low loss constants Factor, the cured finished molded part by setting the appropriate Amounts of the two fillers in the composition is achievable. For better Adhesion between the fillers and the resin are preferably coupling agents, z. As silanes used.

A hardener is preferably added to the composition to facilitate curing accelerate. When the composition is heated, the hardener decomposes to to form free radicals, which then trigger the crosslinking of the polymer chains. preferred Hardeners are organic peroxides, z. Luperox, dicumyl peroxide and t-butyl perbenzoate, all are available.

Basically, the thermoset compositions are processed as follows.

First, all components (polybutadiene or polyisoprene resin, thermoplastic Elastomer, fillers, coupling agent) carefully in a conventional mixer mixed together with a peroxide hardener. The mixing temperature will be like that adjusted that a stronger decomposition of the hardener (and thus a premature curing) be avoided. The mixing is continued until the filler is homogeneously dispersed in the resin.

The homogenized mixture is then removed, cooled and into particles for Milled shapes. Then the particles are poured into a mold, pressed or sprayed, z. B. in a press, injection molding or transfer molding (transfer) mold  or an extruder, and the material is formed into the desired shape. The molding is then cured in two stages in a cross-linked thermoset molding. First, the molding is in a conventional peroxide curing step cured at typical curing temperatures of 150-200 ° C. Subsequently For example, the peroxide cured molding is subjected to high temperature curing to increase the crosslink density. The temperature is above about 250 ° C, but below the decomposition temperature of the resin (typically about 400 ° C). The molding then becomes removed and cooled.

The high-temperature curing gives the finished molding an unusual high degree of networking. Mold compositions in which the thermoplastic Elastomer a polybutadiene or polyisoprene block with less than 50 wt .-% 1,2-addition are suitable, as well as compositions of over 50 wt .-% 1,2-addition. The higher the percentage of 1,2-addition, the greater the Number of hanging vinyl groups participating during the curing reaction can. Thus, the degree of crosslinking of the finished molding after high-temperature curing can be adjusted by selecting the thermoplastic elastomer.

The following thermoset compositions were prepared, molded and cured. All information is in Vol .-%. The cured moldings are hard Plastics with relatively low impact strength.

Example A B3000 resin 21.5 D1102 (low vinyl containing SBS resin, Shell Chemical Corp.) 15.3 TiO₂ 41.3 SiO₂ 18.1 Kevlar 2.0 Luperox peroxide hardener 0.5 t-butyl perbenzoate curing agent 0.2 A180 silane coupling agent (Union Carbide Corp.) 1.0

with the following properties of the finished molding density 2.50 Shrinking (in / in) 0.009 DK pinch waveguide 13.08 DF pinch waveguide 0,003 Bending strength (psi) 13,700 Modulus (Elasticity) × 10⁶ (psi) 1.65 % Water absorption D48 / 50 0.19 Impact strength (ft. Lb / in) 0.40 Thermal expansion coefficient (X) 24-28 ° C-1 (Z) 22-25 Copper adhesion (pli) 1.4

example B

Example A is the same except that D1184, another lower vinyl SBS Resin from Shell, instead of the D1102 resin,

at the following properties of the finished molding density 2.40 Shrinking (in / in) 0,010 DK pinch waveguide 11,50 DF pinch waveguide 0,002 Bending strength (psi) 13,900 Modulus (Elasticity) × 10⁶ (psi) 1.49 % Water absorption D48 / 50 0.13 Impact strength (ft. Lb / in) 0.45 Thermal expansion coefficient (X) 27-31 ° C-1 (Z) 28-29 Copper adhesion (pli) 1.6

Claims (14)

1. shaping method for hard moldings,
marked by

• a) moldable thermoset composition with
  • - Polybutadiene or polyisoprene liquid resin with
    • below 5000 molecular weight and
    • - min. 50 wt .-% 1,2-addition and
  • - thermoplastic elastomer with
  • - first block copolymer
    • With
      Y = polybutadiene or polyisoprene block,
      X = thermoplastic block,
      m, n = average number of blocks in the polymer,
      m = 0 or 1,
      n = min. 1;
• b) shaping the composition into a mold, wherein
  • - The thermoplastic elastomer
    • - Maintains the mold during the molding process and
  • - the liquid resin
    • - keeps the viscosity of the composition low enough for the mold to be easily moldable; and
• c) curing the composition to produce the molding
  • - by high-temperature curing
    • - above about 250 ° C and
    • below the decomposition temperature of the composition.

2. The method according to claim 1,
characterized in that

• the polybutadiene or polyisoprene block
  • - has a large number of hanging vinyl groups available for networking.

3. The method according to claim 1,
characterized in that

• the polybutadiene or polyisoprene block
  • - Has less than 50 wt .-% 1,2-addition.

4. The method according to claim 1,
marked by

• - the composition with
• second block copolymer
  • With
    Z = polyethylene or ethylene-propylene copolymer block,
    W = thermoplastic block,
    p, q = average number of blocks in the copolymer,
    p = 0 or 1,
    q = min. 1.

5. The method according to claim 1 for the production of a dielectric molding,
characterized in that

• Dielectric filler
  • - added to the composition,
  • to impart a given dielectric constant to the molding, and
• - The thermoplastic elastomer
  • - Maintains the filler dispersed substantially uniformly in the composition.

6. The method according to claim 5,
marked by

• a number of fillers of different dielectric constant
  • - in such proportions,
  • - That the molding receives a given dielectric constant.

7. The method according to claim 5 or 6,
characterized in that

• - The cured molding
  • - Is provided with a metal layer
    • with a given coefficient of thermal expansion, and
• - During the molding of the molding
  • Filler and amount are chosen such
    • - That the molding has a thermal expansion coefficient substantially equal to the metal layer.

8. The method according to claim 1,
characterized in that

• - Crosslinking agent
  • - added to the composition.

9. The method according to claim 8,
characterized in that

• - the crosslinking agent has:
  • Triallyl cyanurate,
  • - diallyl phthalate,
  • Divinylbenzene,
  • polyfunctional acrylate monomer or
  • - Combination of it.

10. The method according to any one of the preceding claims,
characterized in that

• - the liquid resin
  • - Polybutadiene is, and
• - the first block polymer
  • is a styrene-butadiene-styrene triblock copolymer.

11. The method according to claim 4,
characterized in that

• - the liquid resin
  • - polybutadiene is,
• the first block copolymer
  • is a styrene-butadiene-styrene triblock copolymer, and
• the second block copolymer
  • is a styrene-ethylene-propylene-styrene triblock copolymer.

12. The method according to claim 1,
characterized in that

• - the composition before the high-temperature curing
  • - catalytic curing
    is subjected to the temperature of high-temperature curing.

13. The method according to any one of claims 5-12,
characterized in that

• - the filler has:
  • - titanium dioxide,
  • Barium titanate,
  • - strontium titanate,
  • - silica / silica,
  • - corundum,
  • - wollastonite,
  • Polytetrafluoroethylene,
  • - glass fibers,
  • - aramid fibers,
  • - Ba₂Ti₉O₂₀,
  • - glass balls,
  • - quartz,
  • - boron nitride,
  • Aluminum nitride,
  • - silicon carbide,
  • Beryllium oxide BaO-PbO-Nd₂O₃-TiO₂,
  • - Magnesium oxide or
  • - Combination of it.

14. molding, producible by the method according to any one of the preceding claims.