JPS60244511A - Reactive injection molding method - Google Patents

Abstract

PURPOSE:To prepare a molded product of which the synthetic resin part is not contracted even under cooling, by compounding a thermally expansible microcapsule with a synthetic resin and expanding the same at the time of injection molding. CONSTITUTION:0.001-2pts.wt. of a thermally expansible microcapsule (e.g., a capsule obtained by encapsulating a hydrocarbonaceous inflating agent by a vinylidene chloride/acrylonitrile copolymer) with an average particle size of 200mum or less is compounded with 100pts.wt. of a polyurethane elastomer. When the thermally expansible microcapsule is expanded by het supplied from a mold at the time of molding, the reactive polyurethane elastomer is reacted and cured to obtain a synthetic resin molded product containing the expanded thermally expansible microcapsule. Even if the molded product is taken out of the mold and cooled, the contraction thereof is suppressed by the expanded microcapsule and the molded product free from a sink mark together with contraction is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reaction injection molding method for manufacturing a cell-containing synthetic resin molded article, and in particular to a method for molding a polyurethane elastomer using raw materials containing thermally expandable microcapsules. The present invention relates to a reaction injection molding method for manufacturing articles.

The production of synthetic resin molded articles by reaction injection molding is well known, and is widely used in particular for the production of polyurethane resin molded articles including polyurethane elastomers. Application to synthetic resins other than polyurethane resins is also known; for example, application to polyamide resins, epoxy resins, unsaturated polyester resins, etc. is being considered, and some of them have been put into practical use by zero-reaction injection. The molding method involves mixing at least two fluid raw materials that can rapidly react to form a synthetic resin when mixed, immediately before a mold, and immediately injecting the synthetic resin into the mold. This is a molding method that focuses on forming Mixing of fluid raw material components is usually carried out by impingement mixing, and in order to achieve more uniform mixing, it is also common to inject the mixture into a mold through an after-mixing mechanism. below,
A mixture of at least two flowable raw material components is referred to as a reactive mixture. Further, although the present invention will be mainly described below with respect to the case where a polyurethane elastomer molded article is produced by a reaction injection molding method, application to other polyurethane synthetic resins or other synthetic resins is not denied.

By reaction injection molding using at least two components: a raw material component containing a high molecular weight active hydrogen compound such as a relatively high molecular weight polyol, a chain extender, and optionally a catalyst and a blowing agent, and a raw material component containing a polyisocyanate compound. Methods for producing polyurethane elastomers such as polyurethane elastomers and polyurethaneurea elastomers are known. Typical examples of high molecular weight active hydrogen compounds are relatively high molecular weight polyols, especially polyether polyols.

The chain extender is a relatively low molecular weight polyhydric alcohol or polyamine, which is also a type of active hydrogen-containing compound.

The use of a catalyst is usually essential and is usually added to the active hydrogen compound-containing raw material component, but it can also be added to the isocyanate compound-containing raw material component. The use of a small amount of a blowing agent such as a halogenated hydrocarbon blowing agent to produce a microcellular polyurethane elastomer is a commonly used means for improving moldability. The density of the microcellular polyurethane elastomer obtained using this small amount of blowing agent is usually 0.
8 g/cvd or more, especially about 0.9 g/- or more. Unless particularly large amounts of reinforcing fibers, flaky fillers, or powder fillers are blended, the upper limit is usually 1.2 g/cn+ or less, particularly about 1.15 g/cn+ or less. The density of the non-foamed polyurethane elastomer is also typically within the above range. In addition, the active hydrogen-containing compound-containing raw material component is divided into two or more parts, and the isocyanate compound-containing raw material component and the raw material component containing the isocyanate compound are divided into three parts in total.
It is also known to carry out reaction injection molding using more than one component.

One problem with polyurethane elastomer molded products obtained by reaction injection molding is their dimensional stability.

For example, problems such as expansion and thermal deformation due to water absorption are well known. Glass # to improve the dimensional stability of polyurethane elastomers! A method of increasing the rigidity of a molded article by blending an mttttt-like filler such as fiber is also known.

However, a problem that has not been studied much in the past is the problem of thermal shrinkage of molded products.Reactive mixtures harden with heat generation in the mold, and molded products are usually removed before they are sufficiently cooled. It will be done. Furthermore, the mold is often heated, and a molded product that is taken out before it has sufficiently cooled usually shrinks as it cools. In order to prevent the Q deformation of the molded product due to this shrinkage, the method of increasing the rigidity of the molded product by adding a filler is effective to some extent, but there are cases in which the problem cannot be solved satisfactorily. For example, when it is difficult to incorporate fibrous fillers for various reasons (for example, when the purpose is to reduce weight)
Needless to say, as the shape of the molded product becomes more complex, defects such as sink marks are more likely to occur on the back surface of the ribs and bosses of the molded product. Such defect t4 is well known in the production of FRP (fiber reinforced thermosetting resin) molded products by press molding such as SMC (sheet molding compound). In manufacturing FRP molded products, this shrinkage problem is solved by blending a low-shrinkage agent made of a thermoplastic polymer or the like with a thermosetting resin (usually an unsaturated polyester resin). However, in reaction injection molding, even in reaction injection molding of unsaturated polyester resins, the use of such low shrinkage agents poses various problems.

For example, in reaction injection molding, it is difficult to use additives that increase the viscosity of a fluid synthetic resin raw material component, and since the internal mold pressure during molding is low, the effect of a low-shrinkage agent may not be fully demonstrated. When manufacturing polyurethane-based elastobu molded products by reaction injection molding, unlike unsaturated polyester-based resins, the application of low-shrinkage agents has not been sufficiently studied.

When applied to polyurethane elastomers, additives must be difficult to react with polyols and polyisocyanate compounds, do not significantly increase their viscosity, dissolve or disperse almost uniformly with them, and be difficult to separate. It is required to satisfy various requirements such as not clogging or abrading piping or mixing and injection equipment (usually called a high-pressure foaming machine), and not inhibiting the polyurethane forming reaction. .

The inventors have conducted various research studies on measures to suppress shrinkage of molded products, particularly in reaction injection molding of polyurethane elastomers. In order to suppress shrinkage of molded products, it is considered effective to use additives that can expand with heat. However, since the aforementioned low-shrinkage agents for unsaturated polyester resins do not exhibit sufficient shrinkage-lowering effects in reaction injection molding, we investigated additives for foaming properties. As foamable synthetic resin particles, synthetic resin particles impregnated with a vaporizable blowing agent of a low-boiling liquid such as polystyrene beads are known. However, ordinary polystyrene beads have a large particle size and cannot be applied to a high-pressure foaming machine, and when the particle size is reduced, the vaporizable blowing agent becomes more volatile and stable foaming becomes difficult.

Further, polystyrene has the problem of being easily dissolved in halogenated hydrocarbon blowing agents used in the production of microcellular polyurethane elastomers. Furthermore, it is also possible to use decomposable blowing agents that generate gases such as nitrogen when decomposed, but decomposition of decomposable blowing agents generally requires a high temperature and a relatively long decomposition time. It is difficult to apply to reaction injection molding which cures, and decomposable blowing agents that decompose at low temperatures have insufficient stability. Furthermore, decomposable blowing agents may generate chemically active groups that may affect reactions in reaction injection molding.

The present inventor conducted various research studies to solve the above problems, and as a result, thermally expandable microcapsules caused shrinkage (
We have discovered that it can be surprisingly effective in reducing the appearance of sink marks (also known as sink marks). Thermally expandable microcapsules are microcapsules that have a foaming agent as a core and a synthetic resin as a shell, and the shell is softened by heat and becomes expandable. The core is usually a vaporizable blowing agent consisting of a hydrocarbon, halogenated hydrocarbon, or other low boiling liquid, but may also be a decomposable blowing agent such as azobisisobutyronitrile. The blowing agent vaporizes or generates gas due to heat, and the microcapsule expands as the shell softens.The relationship between foaming and heat is controlled by the type of blowing agent and the type of synthetic resin in the shell (i.e., its softening temperature). I can do it. Since the microcapsules are not normally destroyed by expansion, they have no effect on the synthetic resins used in reaction injection molding or their raw materials other than the synthetic resin of the shell, which is usually inert against them. Yes (because it needs to be insoluble in the core blowing agent). In order to be applicable to reaction injection molding, the particle size must be small.

In particular, an average particle size of about 200 microns or less is required, and many thermally expandable microcapsules meet this requirement.

The present invention is a reaction injection molding method characterized by using the above thermally expandable microcapsules, that is, a method for producing synthetic resin molded articles by reaction injection molding, in which at least one raw material component has an average particle size of about 200 ml. A reaction injection molding method characterized by blending thermally expandable microcapsules of micron size or less and expanding the thermally expandable microcapsules when a reactive mixture is cured.

It is.

In the present invention, when a reactive mixture containing thermally expandable microcapsules (i.e., a mixture of two or more raw material components) is cured in a mold, the reaction heat of the reactive mixture and, if necessary, the heat supplied from the mold. When the thermally expandable microcapsules are expanded by such methods, the reactive mixture reacts and hardens, yielding a synthetic resin molded article containing expanded thermally expandable microcapsules. When the molded product is taken out of the mold and cooled, the expanded thermally expandable microcapsules suppress the shrinkage of the synthetic resin portion, resulting in a molded product with less shrinkage and shrinkage. The reason for suppressing the shrinkage of the molded product is not necessarily clear, but it is thought that the expanded thermally expandable microcapsules are difficult to shrink even when cooled, and that there is residual expansion force.

In the present invention, the synthetic resin obtained by reaction injection molding is hereinafter also referred to as a matrix, and as described above, the matrix may be foamed or non-foamed.
A preferred matrix is a microcellular or non-foamed polyurethane elastomer, and this matrix will be mainly described below. Thermally expandable microcapsules are preferably used in the same way as fillers in the production of polyurethane elastomers by reaction injection molding, that is, the thermally expandable microcapsules are pre-blended with at least one of two or more raw material components. It is preferably used, for example, in combination with one or both of the active hydrogen compound-containing component and the polyisocyanate compound-containing component. In addition, the method of blending the thermally expandable microcapsules with the above raw material components is not particularly limited, such as blending it in advance with a high molecular weight polyol and mixing it with other raw materials to produce an active hydrogen compound-containing component. Basically, it does not expand in the raw material components, but expands during the curing of the mixture of raw material components, ie, the reactive mixture. Therefore, even if the raw material components are heated (usually heated for reasons such as improving fluidity), it is preferable that the raw material components do not easily expand at that temperature, but they will expand to some extent. is acceptable. Reactivity mixtures usually generate heat of reaction during curing, and it is necessary that the thermally expandable microcapsules expand under these temperature conditions. However, since the temperature inside the mold can be increased by heating the mold, it is not necessary that the expansion occur only due to the heat of reaction.

Thermally expandable microcapsules themselves are well known (see, for example, Japanese Unexamined Patent Publication No. 113338/1983), and some are commercially available.6 In the present invention, the average particle size of the thermally expandable microcapsules is approximately 200 microns. and preferably within the range of about 1 to 100 microns, with a particularly preferred average particle size of about 5 to 100 microns.
It is 50 microns. The expansion start temperature volume (temperature at which the thermally expandable microcapsule expands to approximately double) is preferably approximately 60°C or higher, particularly approximately 80°C or higher. temperature achieved) is about 80-200°C, especially about 100-180'
T:! The maximum expansion ratio is preferably about 5 times or more by volume, particularly about 10 to 100 times.

However, in the present invention, it is not an essential requirement that the temperature during curing of the reactive mixture reaches this maximum expansion temperature;
In addition, it is not essential that the expansion of the thermally expandable microcapsules used reaches the maximum expansion rate; the above expansion start temperature, maximum expansion temperature, and maximum expansion magnification are for the thermally expandable microcapsules alone. It is not necessarily the same temperature or magnification in the reactive mixture, for example, because the reactive mixture in the mold is usually pressurized to some extent.

In that case, the maximum expansion coefficient is usually lower than that in the case of thermally expandable microcapsules alone.

The thermally expandable microcapsules are preferably microcapsules that contain a vaporizable blowing agent made of a low-boiling liquid (hereinafter referred to as the blowing agent to distinguish it from the matrix blowing agent) and have a shell made of a synthetic resin.The blowing agent is carbonized. Hydrogen-based or halogenated hydrocarbon-based expanding agents are suitable. The shell is preferably made of a synthetic resin from which these swelling agents are less leached (it may become leachable after II expansion), and is made of a synthetic resin that is inert to the raw materials used in reaction injection molding (does not easily dissolve or swell). ) is preferred, but even if it is not inert to one of the two or more raw ingredients, it can be incorporated into the other raw ingredients so that it is vigorously reacted in the reaction mixture until it hardens. Preferred shell materials are homopolymers of monomers such as vinyl chloride, vinylidene chloride, acrylonitrile, (meth)acrylic acid esters, etc., and are not necessarily inert to all raw materials unless they are attacked. Copolymers or cobo-limers of one of them with styrene, vinyl acetate, butadiene, etc. are suitable, and their combination with cross-linking monomers such as divinylbenzene is preferred.A particularly preferred shell material is acrylonitrile-chloride. It is a copolymer of at least three vinylidene-crosslinkable heptamers.

The heat-expandable microcapsules may be gas-containing microcapsules in which the microcapsules encapsulating the vaporizable blowing agent made of the above-mentioned low boiling point liquid are expanded to some extent. In this case, the expanded microcapsules need to be able to expand further under the temperature conditions within the mold. It goes without saying that the size of the somewhat expanded and further expandable microcapsules must be less than about 200 microns, preferably less than about 100 microns. Its expansibility alone is at least about 1.5
Similarly, the heat-expandable microcapsules of the present invention are preferably capable of further expansion to a volume twice as large, preferably at least about twice as large. These hollow thermally expandable microcapsules usually have a low specific gravity, but in order to be applicable to the present invention, their specific gravity must be about 0.01 or more. is preferable, and particularly preferably about 0.05 or more. 0 When thermally expandable microcapsules having a low specific gravity are added to a raw material component such as a polyol, they tend to float and separate from the raw material component. However, even if the −1 specific gravity is small, a practically stable dispersion state may be obtained if the viscosity of the raw material components is high, and on the other hand, the small specific gravity makes it easy to exhibit the effect even if the added weight is small.

As mentioned above, it is also possible to use hollow thermally expandable microcapsules, but in the present invention, more preferable thermally expandable microcapsules are microcapsules with a specific gravity of about 0, e to 1.3, and a more preferable specific gravity is Approximately 0.8-1.2
In particular, heat-expandable microcapsules having a specific gravity within the range of about 0.8 to 1.1 are preferred, since the specific gravity of the raw ingredients is typically within the range of 1.0±0.1 (without fillers). This is because it is advantageous in terms of long-term stability (difficulty in separation) of the raw material components for thermally expandable microcapsules, as they are often used (except when blended in relatively large amounts). These high specific gravity thermally expandable microcapsules usually contain the low boiling point liquid as an expanding agent.

The amount of heat-expandable microcapsules to be blended is not particularly limited, but is about 0.00 parts by weight or more, especially about 0.01 parts by weight or more based on all raw material components (i.e., reactive mixture) excluding heat-expandable microcapsules. is preferred, and the upper limit is preferably about 20 parts by weight, preferably about 0.01 to 10 parts by weight, particularly about 0.0
The amount of thermally expandable microcapsules is preferably 5 to 5 parts by weight. In the examples described later, the entire amount of thermally expandable microcapsules is blended with the active hydrogen compound-containing component, but as described above, it may also be blended only with the polyisocyanate compound-containing component. It can also be blended into the ingredients, and is not limited to the method of the example. In addition, if a third component is used, it can also be blended into it. In the present invention, the matrix is The matrix is not limited to polyurethane elastomers, and may be any of the various synthetic resins mentioned above to which reaction injection molding can be applied, and the matrix may be foamed. Furthermore, the density of the matrix itself excluding the expanded heat-expandable microcapsules (apparent density including air bubbles) is not particularly limited, but is approximately 0.4 g.
/cn? Above, especially about 0. It is preferable that f1g/cr+ or more, and the upper limit is about 1.5g/cn? is appropriate. If the matrices and glue are made of polyurethane elastomer, the weight is about 0.8 to 1.2 g/cm as mentioned above. is preferred.

The density of the obtained molded product containing expanded thermally expandable microcapsules is not particularly limited, but is about 0.2 g/cnl or more.
However, about 0.4 g/- or more is particularly preferred. For polyurethane elastomers, it is preferably about 0.8 g/d or more, particularly about 0.8 g/cv1 or more. The upper limit of the density varies depending on whether or not fillers are used, but even if fillers are used, it is approximately 1.3 g/cm, especially approximately 1.28 g/cm.
c-ffl is suitable.

Below, an outline of the raw material will be explained when the matrix is a microcellular or non-foamed polyurethane elastomer.

As the high molecular weight active hydrogen compound, a high molecular weight polyol having two or more hydroxyl groups is suitable. However, it is also known to use high molecular weight active hydrogen compounds having two or more amine groups or an amine group and a hydroxyl group, such as those having an amide 7 group at the end as described in JP-A-58-103521. Polyoxyalkylene compounds (hereinafter referred to as aminated polyethers) can also be used. The average molecular weight per active hydrogen-containing group (i.e., hydroxyl group and/or amino group) of the high molecular weight active hydrogen compound is about 60
The number of active hydrogen-containing groups per molecule is preferably 0 to 3,000, particularly about 800 to 2,000, and the average number of active hydrogen-containing groups per molecule is preferably 2.0 to 4.0, particularly about 2.0 to 3.5. be. As the high molecular weight active hydrogen compound, polyether polyols, mixtures of polyether polyols as main components with other high molecular weight polyols, and polymer polyols based on polyether polyols are most preferable.As polyether polyols, polyvalent vinyl Polyether polyols obtained by adding a monoepoxide such as fullkylene oxide or tetrahydrofuran to an ether are suitable, and in particular, polyether polyols obtained by adding propylene oxide and/or butylene oxide to a polyvalent oxide together with ethylene oxide are suitable. For polyols to be suitable for zero-reaction injection molding, the presence of highly reactive hydroxyl groups, i.e. primary hydroxyl groups, is necessary, and in the case of monoepoxy-based polyether polyols there are usually at least about The presence of 5% by weight of oxyethylene groups is considered almost essential.

The higher the proportion of terminal oxyethylene groups, the higher the proportion of primary hydroxyl groups and the higher the reactivity, but the higher the proportion of oxyethylene groups, the higher the hydrophilicity of the polyether polyol, which in turn increases the water absorption of the polyurethane elastomer. becomes high, causing a decrease in water absorption dimensional properties. Therefore, the upper limit of the presence of oxyethylene groups in the polyether polyol is suitably about 35% by weight, particularly about 25% by weight.
is preferred. However, this is not the case when producing hydrophilic polyurethane. It is almost essential that at least 5% by weight of oxyethylene groups be present at the ends of the polyether chains, but they may also be present inside the polyether chains. The polyether polyol may be a mixture of two or more polyether polyols having different numbers of hydroxyl groups and molecular weights, and in particular, these two polyether polyols whose main component is polyether diol or polyether triol.
Seeds or mixtures with other polyether polyols are preferred.

The polymer polyol is preferably a polymer polyol based on a polyether polyol as described above. Particularly preferred are polymer polyols obtained by polymerizing at least one of acrylonitrile, styrene, and other vinyl monomers in a polyether polyol;
Polyether polyols containing unsaturated groups, polymer polyols obtained by polymerizing vinyl monomers in polyether polyols, polyols containing condensation polymers obtained by condensation polymerization in polyether polyols, and other polyols containing polymer components. can also be used. Other high molecular weight polyols that can be used in combination with polyether polyols include hydroxyl group-containing hydrocarbon polymers such as butadiene homopolymers and copolymers having two or more hydroxyl groups, and polyester polyols. is effective in improving the water absorption dimensional properties of polyurethane elastomers. The aminated polyether is a compound obtained by aminating some or all of the hydroxyl groups of the polyether polyol or polyether polyol that does not have an oxyethylene group at the end, and is a compound obtained by aminating some or all of the hydroxyl groups of the polyether polyol or polyether polyol that does not have an oxyethylene group at the end, and is It can be used in combination with ether polyol etc.

In the production of polyurethane elastomers, low molecular weight active hydrogen compounds, ie, chain extenders (trivalent or higher valent compounds are sometimes referred to as crosslinking agents), are usually used in combination with the above-mentioned high molecular weight active hydrogen compounds. However, the chain extender is not an essential raw material, and the chain extender may not be used.6 As the chain extender, a low molecular weight polyol or polyamine is suitable. The molecular weight is preferably about 400 or less, particularly about 200 or less. The polyol is most preferably ethylene glycol or 1,4-butanediol, and other
It is also possible to use alcohols with higher valences or higher, polyether polyols with low molecular weights, alkanolamines, and the like.

Examples of polyamines include aromatic diamines, low-molecular cap aminated polyethers, and other polyamines, and halogen-substituted or alkyl group-substituted aromatic diamines are preferred, with halogen-substituted or lower alkyl group-substituted diaminobenzenes being particularly preferred.As the catalyst, A tertiary amine catalyst or an organic tin catalyst is preferred, and both are usually used in combination. Although the use of a catalyst is usually essential, it is not necessarily required when using high molecular weight aminated polyethers with high amination rates.

Modified or unmodified aromatic polyisocyanates are suitable as the polyisocyanate compound, and in some cases, other polyisocyanate compounds may be used alone or in combination with aromatic polyisocyanates and the like. As the aromatic polyisocyanate, diphenylmethane diisocyanate, polymethylene polyphenylisocyanate, tolylene diisocyanate, etc. are suitable, and diphenylmethane diisocyanate consisting of 4,4'-diphenylmethane diisocyanate and its isomers is particularly suitable. Although these can be used as unmodified products, it is common to use modified products for application to reaction injection molding methods. Modified products include, but are not limited to, prepolymer-type modified products and carbodiimide-type modified products. The amount of polyisocyanate compound used is approximately 9 in terms of incyanate index.
0 to 120, especially about 85 to 110 are suitable.

The use of catalysts is usually essential in the production of polyurethane elastomers. A tertiary amine catalyst or an organotin compound is usually used in the process, and a blowing agent is often used to improve the filling of the reactive mixture into the mold. However, in the present invention, a polyurethane elastomer similar to a foam can be obtained by using thermally expandable microcapsules, and since the use of parentheses also has the effect of improving filling properties, the use of a blowing agent is not necessarily essential, and a small amount of foaming is required. The polyurethane elastomer obtained using this agent is called a microcellular (polyurethane) elastomer.Blowing agents include trichlorofluoroethane, methylene chloride, other halogenated hydrocarbon blowing agents, and water. are often used together. It is particularly preferable to use a halogenated hydrocarbon blowing agent, and the amount thereof is preferably about 15 parts by weight or less, particularly about 2 to 10 parts by weight, per 10 parts by weight of the high molecular weight active hydrogen compound.

The polyurethane elastomer can be produced by using any additives in addition to the above raw materials. Examples of the optional additives include internal mold release agents, fillers, colorants, ultraviolet absorbers, light stabilizers, These include antioxidants and flame retardants. Examples of fillers include inorganic fibers such as glass fibers and wollastonite, organic fibers such as synthetic fibers, calcium carbonate, other powder fillers, buoys, and other flat fillers. As the amount of these fillers increases, problems arise with the viscosity and operability of the raw material components, so it is preferable that the amount of these fillers be less than about 30% by weight, especially less than 20% by weight, based on the total synthetic resin raw material. Mainly contains active hydrogen compounds #
However, those that are non-reactive with incyanate groups can also be blended with the incyanate compound-containing raw material component.

The synthetic resin molded article obtained by the present invention, particularly the polyurethane elastomer molded article, can be used for various purposes.

It is particularly suitable for automobile exterior parts, such as bumper shells, fascias, fenders, and door panels. However, the applications are not limited to this, and may also be used in other automatic military components, electronic or electronic equipment housings, and other applications.

EXAMPLES The present invention will be specifically explained below using Examples, but the present invention is not limited to these Examples.

Example ■, using the following raw materials, length 1800 ms, wall thickness 3.5
An automobile bumper outer shell weighing about 4 kg was manufactured by reaction injection molding.

Polyol component polyoxypropylene oxyethylene triol (polyol with a molecular weight of approximately 8,500 containing 15% by weight of oxyethylene groups at the end)
84 parts by weight Ethylene glycol 16 Triethylenediamine solution (“Tab: l 33LV”) 0.4 // Dibutyltin dilaurate 0.08 // Trichlorofluoromethane 5
〃 Thermally expandable microcapsules [Description] Incyanate component carbodiimide-modified diphenylmethane diincyanate (NGO content 28%) [The amount used is the amount that will give an NGO index of 105 Type of thermally expandable microcapsules Heat expandable microcapsule A: Product Name: r Matsumoto Microsphere-F-5QJ
[Manufactured by Matsumoto Yushi Seiyaku] Average particle size: Approximately! 5 microns (more than 95% of them are 5-3
(within the range of 0 microns) Shell material and its softening temperature: vinylidene chloride-7crylonitrile copolymer, 100-105°C Expansion agent: hydrocarbon expansion agent Maximum expansion rate and temperature: about 20 times, about 140 °C True specific gravity after drying: Approx. 1.02 Thermal expandable microcapsule B: Product name: "Fumoto Microsphere-F-304 [
Made by Matsumoto Yushi Seiyaku ■] Average particle size: Approximately 15 microns (more than 95% of them are 5-3
(within the range of 0 microns) Shell material and its softening temperature: Vinylidene chloride-acrylonitrile copolymer (however, the composition ratio is different from that of thermally expandable microcapsules A) 75-85°C Expansion agent dihydrocarbon System expansion agent Maximum expansion coefficient and temperature: Approximately 75 times, approximately 135°C True specific gravity after drying: Approximately 1.02 II, Molding and evaluation Type and amount of thermally expandable microcapsules [parts by weight in polyol component] As shown in Table 1, molded products with a density of 1.05 g/- and a density of 1.05 g/- were molded by changing the amount of the reactive mixture filled in the mold. Three days after molding, the appearance was visually evaluated (judgment criteria are shown in the numerical values below), and after three days of molding, the molding shrinkage rate of the molded product with a density of 1.05 g/cn+ was measured. These results are shown in Table 1. For reference, the physical properties of a molded article with a specific gravity of 1.05 g/cnl are listed in Table 1.

Appearance Judgment Criteria 5: No sink marks 4: Slight sink (only around the gate) 3: Medium sink (〃) 2: Heavy sink (around the gate and central surface) 1: Heavy sink (over the entire surface of the molded product)

Claims (1)

[Claims] 1. In a method for producing a synthetic resin molded article by reaction injection molding, at least one raw material component has an average particle diameter of 200
Contains thermally expandable microcapsules of less than a micron size,
A reaction injection molding method characterized in that the thermally expandable microcapsules are expanded during curing of the reactive mixture. 2. The thermally expandable microcapsules are synthetic resin microcapsules containing a vaporizable expanding agent, and the temperature at which the thermally expandable microcapsules can achieve their own maximum expansion ratio is within the range of about 80 to 200°C. Claim 1. 3. Thermal expandable microcapsules have an average particle size of 1 to 100
The method according to claim 1, characterized in that the thermally expandable microcapsules have a density of 0.01 to 1.3 g/ant. 4. Claims characterized in that the blending amount of the thermally expandable microcapsules is 0.001 to 20 parts by weight based on 100 parts by weight of the reactive mixture excluding the thermally expandable microcapsules. Method of Section 1.