JP5003905B2 - Method for producing silicone rubber foam - Google Patents

Description

The present invention relates to the production how silicone rubber foam by injection molding.

  Silicone rubber is used as a rubber molded product in various fields by making use of heat resistance, cold resistance, electrical characteristics, and the like. The liquid addition curable silicone rubber composition has many achievements in injection molding processing, such as automating injection molding, shortening the molding cycle, and cost reduction of molded products. In recent years, high-safety silicone rubber foams that take into account the needs in the home appliance and food fields, including improved heat storage of rubber molded products by injection molding, weight reduction of rubber molded products, and environmental considerations for rubber molded products It was desired to develop a body.

  Conventionally, in thermoplastic resin (plastics) materials, there is a trend to introduce supercritical fluids and develop plastics foams, but about silicone rubber foams by injection molding of liquid addition curable silicone rubber compositions Not reported.

  For example, Japanese Patent No. 2625576 (Patent Document 1) discloses a method of continuously introducing a supercritical liquid into a polymer plastics material and foaming the polymer plastics material, but does not describe a liquid silicone rubber composition. Absent.

In Japanese Patent No. 3506543 (Patent Document 2), after a gas is dispersed in an uncured or semi-cured reaction curable resin at a critical temperature or higher and a critical pressure or higher, the pressure is 10 kgf / cm ² / sec or higher. A method is disclosed in which foaming is performed at a speed of, foamed in an uncured or semi-cured state, and then cured. This method is effective for a milable type composition of silicone rubber (that is, a semi-solid that does not flow at room temperature), and is supplied with a crumbly-type (semi-solid) composition of silicone rubber to a pressure vessel. A method is described in which a state gas is injected and foamed and cured by adjusting the pressure.

  However, in the injection molding of a liquid addition curable silicone rubber composition, there is usually a problem that the material is still fluid in an uncured or semi-cured state, and it is difficult to foam uniformly in this state. So far, no effective method for producing a uniformly foamed silicone rubber foam by injection molding of a liquid addition-curable silicone rubber composition has been reported.

Japanese Patent No. 2625576 Japanese Patent No. 3506543

The present invention has been made in view of the above circumstances, by injection molding of liquid addition-curable silicone rubber composition having a uniform cell, to provide a manufacturing how the good reproducibility silicone rubber foam For the purpose.

  As a result of intensive studies in order to solve the above-mentioned problems, the present inventors injected a supercritical fluid from a material supply line and injected a mixture of the supercritical fluid and a liquid addition-curable silicone rubber composition. By injecting into a mold cavity under a pressure of less than 100 MPa, foaming and heat-curing, it is found that the resulting silicone rubber foam has a uniform cell and is a highly reproducible production method. That led to

That is, the present invention relates to a silicone characterized in that a mixture obtained by mixing a supercritical fluid and a liquid addition-curable silicone rubber composition is injected into a mold cavity at an injection pressure of less than 100 MPa, and foamed and cured. to provide a manufacturing how the rubber foam.

  According to the present invention, a silicone rubber foam having uniform cells can be formed by injection molding of a liquid addition-curable silicone rubber composition, which can contribute to productivity improvement.

  In the present invention, a mixture obtained by mixing a supercritical fluid and a liquid addition-curing silicone rubber composition is injected into a mold cavity at an injection pressure of less than 100 MPa, and foamed and cured to obtain a silicone rubber foam. To manufacture.

The addition-curable silicone rubber composition that is liquid at room temperature (25 ° C.) applied in the present invention has a conventionally known composition, for example,
(A) an organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule;
(B) an organohydrogenpolysiloxane containing a hydrogen atom (SiH group) bonded to at least two silicon atoms in one molecule;
Examples include (C) fumed silica having a specific surface area of 50 m ² / g or more by BET method, and (D) an addition reaction catalyst as an essential component.

[(A) Alkenyl group-containing organopolysiloxane]
The organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule of the component (A) is usually a known organopolysiloxane used as a base polymer of an addition-curable silicone rubber composition. And has a viscosity of 1 to 100 Pa · s at 25 ° C., preferably 5 to 100 Pa · s, more preferably 10 to 100 Pa · s. When the viscosity of the organopolysiloxane of the component (A) is lower than the above range, the mechanical strength of the silicone rubber foam obtained by curing the composition is lowered, which may cause a practical problem as a foam molded product. is there. On the other hand, when the viscosity is higher than the above range, the viscosity of the composition becomes too high, the supply time by the material pump becomes long, and the productivity may deteriorate. In the present invention, the viscosity can be measured with a rotational viscometer or the like.

This alkenyl group-containing organopolysiloxane usually has the following average composition formula:
R _a SiO _{(4-a) / 2} (I)
(In the formula, R is independently an alkyl group such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, hexyl group, cyclohexyl group, vinyl group, allyl group, propenyl group, Unsubstituted monovalent hydrocarbon groups such as alkenyl groups such as isopropenyl group and butenyl group, aryl groups such as phenyl group, tolyl group and xylyl group, and aralkyl groups such as benzyl group; 3,3,3-trifluoropropyl A substituted monovalent hydrocarbon group such as a substituted alkyl group in which at least a part of the hydrogen atoms of the monovalent hydrocarbon group such as a group or a cyanomethyl group is substituted with a halogen atom or a cyano group. Or may be the same, but it is necessary that the molecule contains two or more alkenyl groups (usually 2 to 50, preferably about 2 to 20). This alkenyl group may be bonded to the silicon atom at the end of the molecular chain, may be bonded to the silicon atom in the middle of the molecular chain (non-terminal of the molecular chain), or may be bonded to both of them. Preferably contains at least alkenyl groups bonded to silicon atoms at both ends of the molecular chain, a is a number in the range of 1.9 to 2.4, preferably 1.95 to 2.05.
What is shown by is used.

This organopolysiloxane may be linear, RSiO _3/2 units (where R is as described above) or branched containing SiO _4/2 units. It consists of repeating diorganosiloxane units R ₂ SiO _2/2 (R is as described above), and both ends of the molecular chain are blocked with a triorganosiloxy group R ₃ SiO _1/2 (R is as described above) A chain diorganopolysiloxane is preferred. The substituent bonded to the silicon atom may be basically any of the above, but the alkenyl group is preferably a vinyl group, and the other substituents are preferably a methyl group or a phenyl group. .

[(B) Organohydrogenpolysiloxane]
The organohydrogenpolysiloxane containing a hydrogen atom (hydrosilyl group represented by SiH) bonded to at least two silicon atoms in one molecule of the component (B) is contained in the alkenyl group-containing organopolysiloxane of the component (A). In the addition (hydrosilylation) reaction between the alkenyl group of (B) and the silicon atom-bonded hydrogen atom (SiH group) in the component (B), the component acts as a crosslinking agent.

  The organohydrogenpolysiloxane is not particularly limited in molecular structure, and various types of conventionally produced, for example, linear, cyclic, branched, and three-dimensional network structures can be used. It contains at least 2 (usually 2 to 200), preferably 3 or more (for example, 3 to 150), more preferably about 4 to 100, hydrogen atoms bonded to each other, that is, SiH groups. is necessary.

The group bonded to the silicon atom other than the SiH group of the component (B) is a substituted or unsubstituted monovalent hydrocarbon group similar to the monovalent hydrocarbon group R of the average composition formula (I), but an alkenyl group. And the like which do not contain an aliphatic unsaturated bond such as methyl group and phenyl group are particularly preferable.
The organohydrogenpolysiloxane of the component (B) has a number of silicon atoms (or polymerization degree) in one molecule of 2 to 300, preferably 3 to 200, more preferably about 4 to 100. Good.

Examples of the (B) component organohydrogenpolysiloxane include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethyltetracyclosiloxane, 1,3,5,7,8. Siloxane oligomers such as pentamethylpentacyclosiloxane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane / dimethylsiloxane cyclic copolymer, tris (dimethylhydrogensiloxy) methylsilane, tris (dimethylhydrogensiloxy) phenylsilane; Trimethylsiloxy group-blocked methyl hydrogen polysiloxane at both ends of the chain, Trimethylsiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer at both ends of the molecular chain, Silanol group-blocked methyl hydrogen at both ends of the molecular chain Polysiloxane, Silanol group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer, Molecular chain both ends dimethylhydrogensiloxy group-blocked dimethylpolysiloxane, Molecular chain both ends dimethylhydrogensiloxy group-blocked methylhydrogenpoly Siloxane, dimethylhydrogensiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer, etc .; R ₂ (H) SiO _1/2 unit and SiO _4/2 unit, optionally R ₃ SiO _{1 / 2} units, R ₂ SiO _2/2 units, R (H) SiO _2/2 units, (H) SiO _3/2 units or RSiO _3/2 units (wherein R is the average composition formula (I ), But preferably does not contain an aliphatic unsaturated bond such as an alkenyl group. It can be exemplified corn resin or the like.

  The blending amount of the component (B) is 0.4 to 5.0 equivalents of SiH groups in the component (B) with respect to one alkenyl group contained in the component (A) (that is, 0.4 to 5.0). Number), preferably 0.8 to 3.0 equivalents (that is, 0.8 to 3.0). When the amount is less than 0.4 equivalent, the crosslinking density becomes too low, which may adversely affect the heat resistance of the foam molded product. On the other hand, when the amount is more than 5.0 equivalents, the problem of foaming due to the dehydrogenation reaction occurs, and the heat resistance may be similarly adversely affected.

[(C) Fumed silica]
The fumed silica which is the component (C) of the present invention is blended to give sufficient strength to the silicone rubber. BET specific surface area of the fumed silica, 50 m ² / g or more, preferably 100 to 400 m ² / g, more preferably 150~350m ² / g. If the specific surface area is less than 50 m ² / g, sufficient strength cannot be obtained, and the appearance of the foam may be deteriorated. If the specific surface area is larger than 400 m ² / g, blending may be difficult.

  These fumed silicas may be used as they are, but those previously treated with a surface hydrophobizing agent may be used, or those treated by adding a surface treating agent during kneading with silicone oil may be used. preferable. These surface treatment agents may be any known ones such as alkylalkoxysilanes, alkylchlorosilanes, alkylsilazanes, silane coupling agents, titanate treatment agents, fatty acid esters, etc. They may be used simultaneously or at different timings.

  Moreover, it is preferable that the compounding quantity of these fumed silicas of (C) component is 10-40 mass parts with respect to 100 mass parts of (A) component, More preferably, it is 15-35 mass parts. If the blending amount is less than 10 parts by mass, sufficient rubber strength may not be obtained, and if it exceeds 40 parts by mass, blending may be difficult.

[(D) Addition reaction catalyst]
(D) Component addition reaction catalyst includes platinum black, platinous chloride, chloroplatinic acid, reaction product of chloroplatinic acid and monohydric alcohol, complex of chloroplatinic acid and olefins, platinum bisacetoacetate, etc. White metal metal catalysts such as platinum-based catalysts, palladium-based catalysts, and rhodium-based catalysts.
The addition amount of the addition reaction catalyst can be a catalytic amount, and is usually about 0.5 to 1,000 ppm, particularly about 1 to 500 ppm as a platinum group metal (in terms of mass) with respect to the component (A).

[Other ingredients]
In the addition curable silicone rubber composition applied at room temperature in the present invention, as other components, if necessary, a filler such as precipitated silica, quartz powder, diatomaceous earth, calcium carbonate, carbon black, conductivity Conductive agents such as zinc white, metal powder, nitrogen-containing compounds and acetylene compounds, phosphorus compounds, nitrile compounds, carboxylates, tin compounds, mercury compounds, sulfur compounds and other hydrosilylation reaction control agents, such as iron oxide and cerium oxide The addition of an internal mold release agent such as a heat-resistant agent, dimethyl silicone oil, an adhesiveness imparting agent, a thixotropic property imparting agent, etc. is optional as long as the appearance of the foam molded product is not impaired.

  In the present invention, a supercritical fluid is used. The supercritical fluid is in a state where the temperature and pressure (critical point) at which the gas and the liquid can coexist is exceeded, and has a property different from that of a normal gas or liquid. Special fluid shown. For example, carbon dioxide, nitrogen, ethane, ethylene and the like can be mentioned. In the injection molding of the liquid addition curable silicone rubber composition, the cylinder part of the molding machine preferably mixes the supercritical fluid and the rubber composition around room temperature, so that the critical temperature is 31 ° C. and the critical pressure is 7.38 MPa. Some carbon dioxide is preferred. Moreover, it is preferable from the safety | security of a silicone rubber foam to use nitrogen whose critical temperature is -147 degreeC and whose critical pressure is 3.35 MPa.

  The mixing amount of the supercritical fluid is preferably 0.1 to 50 parts by weight, more preferably 0.5 to 40 parts by weight, particularly 1 to 30 parts by weight with respect to 100 parts by weight of the liquid addition-curable silicone rubber composition. preferable. If the amount is less than 0.1 parts by mass, the silicone rubber composition may not be a foam. If the amount exceeds 50 parts by mass, abnormal foaming may occur, the physical strength of the foam may be reduced, and it may be difficult to use practically. is there.

Next, the manufacturing method of the silicone rubber foam by injection molding of this invention is demonstrated with reference to drawings.
As shown in FIG. 1, the liquid addition-curable silicone rubber composition is usually used as a material divided into two liquids, liquid A and liquid B. The material divided into the two liquids is supplied from the material supply pumps 1 and 2 to the quantifiers 11 and 12. The A liquid and the B liquid merge from the quantifiers 11 and 12 through the material supply line 3 at a predetermined ratio. The supercritical fluid C is press-fitted from the supercritical fluid supply device 4 into the material supply line 3 where the liquid A and the liquid B merge, and the material A liquid, the liquid B, and the supercritical fluid C are premixed using the static mixer 5. Is done. The premixed material is supplied to the cylinder portion 6 of the injection molding machine, and is rotationally mixed again by the screw mixer 61 while being quantitatively determined. After mixing, it is injected into the mold 7 from the cylinder part 6, heated in the mold and cured together with foaming, and a silicone rubber foam having uniform cells is molded.

  In addition, it is also possible to supply a supercritical fluid directly to the cylinder part of an injection molding machine, without premixing with a static mixer. In this case, the cell diameter of the silicone rubber foam after heat curing may increase and the cell diameter uniformity may decrease. In order to achieve sufficient mixing of the supercritical fluid and the liquid addition-curing silicone rubber composition, the mixing is performed in two stages: a pre-mixing process using a static mixer or the like and a main mixing process using a screw mixer or the like. Preferably it is done.

  In the present invention, the pressure for injecting the material in which the supercritical fluid is injected into the liquid addition-curable silicone rubber composition into the mold cavity is less than 100 MPa (usually 99 MPa or less), preferably 20 to 95 MPa, more preferably 30. It is essential that the pressure be ˜90 MPa. When the mold is filled with a material at a pressure of 100 MPa or more and cured by heat, the cell diameter of the silicone rubber foam after heat curing is increased. However, when injected at a pressure of less than 100 MPa, the cell diameter of the heat-cured silicone rubber foam becomes uniform, and the maximum particle diameter of the cell can be 300 μm or less, preferably 20 to 250 μm, particularly 50 to 200 μm. .

  Thereafter, when the molding material injected into the cavity is cured, the temperature in the mold is usually less than 150 ° C. (that is, 149 ° C. or less, particularly 145 ° C. or less), preferably 70 to 140 ° C., particularly 80 to It is preferable to cure and foam in the mold in a curing temperature range of 130 ° C., particularly 100 to 130 ° C. When cured at a temperature of 150 ° C. or higher, the bubbles of the supercritical fluid may not be assimilated, and foam cells may be difficult to form.

The mold has a ratio L / S (mm / mm ² ) of the maximum flow length L in the cavity to the sectional area S of the gate of the mold exceeding 7.0, usually exceeding 7.0. 30 or less, in particular, more than 7.0 and 20 or less can be used.

  The molded product of the silicone rubber foam obtained by the present invention can be used for packing for food because of its excellent appearance and safety, and for OPC rolls and fixing rolls of printers and copying machines from the viewpoint of practical strength.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not restrict | limited to the following Example. In the following examples, the viscosity is a value measured with a rotational viscometer at 25 ° C.

[Preparation of Liquid Addition-Curable Silicone Rubber Composition]
90 parts by mass of dimethylpolysiloxane having a viscosity of 30 Pa · s (average degree of polymerization of about 750) with fumed silica having a specific surface area of 300 m ² / g sealed at both ends with dimethylvinylsiloxy groups (Nippon Aerosil) 40 parts by mass, Aerosil 300 manufactured by Co., Ltd., 8 parts by mass of hexamethyldisilazane, and 2 parts by mass of water were mixed at room temperature (25 ° C.) for 30 minutes, heated to 150 ° C., and stirred for 3 hours to cool. A silicone rubber base was obtained.

  130 parts by mass of this silicone rubber base, 60 parts by mass of dimethylpolysiloxane having a viscosity of 100 Pa · s (average polymerization degree of about 1,000) at 25 ° C. sealed at both ends with dimethylvinylsiloxy groups, and both ends as a crosslinking agent And methyl hydrogen polysiloxane having a SiH group in the side chain (viscosity 0.011 Pa · s, polymerization degree 20, SiH group amount 0.0050 mol / g) 2.0 parts by mass (SiH group / alkenyl group molar ratio (mol /Mol)=2.2), 0.10 parts by mass of ethynylcyclohexanol and 0.1 parts by mass of platinum catalyst (Pt concentration 1% by mass) are mixed as a reaction control agent so that the crosslinking agent and the platinum catalyst are not mixed. The liquid was divided into two liquids, liquid A and liquid B, to prepare a liquid addition-curable silicone rubber composition.

[Examples 1 and 2]
The prepared liquid addition curable silicone rubber composition of liquid A and liquid B is set in a material supply pump, and liquid A and liquid B are supplied in equal amounts (mass), and the supercritical fluid is supplied to the material supply line. Carbon dioxide heated to 40 ° C. was injected from the supply device at a pressure of 8 MPa. Carbon dioxide in the supercritical state supplied 10 parts by mass in Example 1 and 15 parts by mass in Example 2 with respect to 100 parts by mass of the total amount of materials of Liquid A and Liquid B. The materials of liquid A and liquid B and carbon dioxide in a supercritical state were premixed with a static mixer and supplied to the cylinder part of the injection molding machine. In the cylinder part, the materials of liquid A and liquid B and carbon dioxide in a supercritical state were rotated and mixed again with a screw mixer. A mold having a ratio L / S (mm / mm ² ) of the maximum flow length L (mm) in the cavity to the gate cross-sectional area S (mm ² ) of the mold of 7.1 is used. The mixture was injected at a pressure of 90 MPa and cured at 120 ° C. for 240 seconds to obtain a silicone rubber foam. The density of the obtained foam and the maximum and minimum particle diameters of the foam cells were measured. The results are shown in Table 1.

[Examples 3 and 4]
Similarly to Example 1, nitrogen at a temperature of 23 ° C. was injected into the material supply line from the supercritical fluid supply apparatus at a pressure of 8 MPa. Nitrogen in a supercritical state was injection-molded in the same manner except that 10 parts by mass in Example 3 and 15 parts by mass in Example 4 were supplied to 100 parts by mass of the total amount of materials A and B. Curing was carried out at 240 ° C. for 240 seconds to obtain a silicone rubber foam. The density of the obtained foam and the maximum and minimum particle diameters of the foam cells were measured. The results are shown in Table 1.

[Comparative Examples 1 and 2]
A silicone rubber foam was obtained in the same manner as in Examples 1 and 2 except that the injection pressure to the mold was 120 MPa. The density of the obtained foam and the maximum and minimum particle diameters of the foam cells were measured, and the results are shown in Table 2.

[Comparative Examples 3 and 4]
A silicone rubber foam was obtained in the same manner as in Examples 3 and 4 except that the injection pressure to the mold was 120 MPa. The density of the obtained foam and the maximum and minimum particle diameters of the foam cells were measured, and the results are shown in Table 2.

参考データ：二酸化炭素及び窒素が０質量部の場合、ゴムの密度１．１４ｇ／ｃｍ³

Reference data: When carbon dioxide and nitrogen are 0 parts by mass, rubber density is 1.14 g / cm ³

It is a flowchart which shows the outline of the process of the manufacturing method of the silicone rubber foam of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Material supply pumps 11 and 12 Metering device 3 Material supply line 4 Supercritical fluid supply apparatus 5 Static mixer 6 Cylinder part 61 Screw mixer 7 Mold A A liquid B B liquid C Supercritical fluid

Claims (5)

  A method for producing a silicone rubber foam, characterized in that a mixture obtained by mixing a supercritical fluid and a liquid addition-curing silicone rubber composition is injected into a mold cavity at an injection pressure of less than 100 MPa, and foamed and cured. . A liquid addition-curable silicone rubber composition is
(A) Organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule: 100 parts by mass
(B) Organohydrogenpolysiloxane containing a hydrogen atom (SiH group) bonded to at least two silicon atoms in one molecule: In one component (B) with respect to one alkenyl group contained in component (A) Amount of SiH groups in the range of 0.4 to 5.0 equivalents,
(C) Specific surface area by BET method is 50m ² / G or more fumed silica: 10 to 40 parts by mass, and
(D) Platinum group metal catalyst as addition reaction catalyst: 0.5 to 1,000 ppm as platinum group metal with respect to component (A)
The manufacturing method of Claim 1 which uses as an essential component. The supercritical fluid is selected from carbon dioxide, nitrogen, ethane, and ethylene, and the mixing amount of the supercritical fluid is 0.1 to 50 parts by mass with respect to 100 parts by mass of the liquid addition-curable silicone rubber composition. The manufacturing method according to claim 1 or 2. The supercritical fluid and the liquid addition-curable silicone rubber composition are mixed in two stages, a premixing step using a static mixer and a main mixing step using a screw mixer. Manufacturing method. As a mold, the ratio L / S (mm / mm) of the maximum flow length L in the cavity to the sectional area S of the gate of the mold ² The manufacturing method of any one of Claims 1-4 which uses a thing exceeding 7.0 and 30 or less.

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