JPH04170444A - Expanded plastics and its production - Google Patents

Abstract

PURPOSE:To obtain a resin composition which can give an expanded heat- resistant lowly water-absorptive plastics when heated by mixing a polymer comprising (meth)acrylic acid units and (meth)acrylonitrile units with a specified polymer. CONSTITUTION:100 pts.wt. polymer of a molecular weight of 10,000-500,000, having a ratio of the structural units of formula I (wherein R is H or CH3) to that of formula II (wherein R is as defined above) of 2/3-3/2 (by mole) and a total of the structural units of a formulas I and II of 20wt.% or above is mixed with 1-100 pts.wt. homopolymer and/or copolymer of a molecular weight of 50,000-500,000 represented by the structural units of formula III (wherein R<1> is H or CH3) as a blowing agent. In this way, a resin composition which can give and expanded heat-resistant lowly water-absorptive plastics when heated can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to poly(meth)acrylimide foam (methacrylimide foam or acrylimide foam, hereinafter referred to in the same manner) obtained by heating. This invention relates to converted foamed plastics that are heat resistant and have low water absorption.

[Problems to be solved by the prior art and the invention] Thermoplastic resins such as polyurethane foam, polystyrene foam, and polyvinyl chloride foam have traditionally been used as foam materials for heat insulation or sound insulation. Foams are known. In recent years, these foamed materials have been used as structural materials for airplanes, ships, etc., ie, as core materials for composite sandwich boards. This is due to the difficulty in adhering or repairing conventionally used honeycomb structures. However, conventional foam materials cannot withstand the molding temperatures or pressures of sandwich structures.

Various studies are being conducted on these issues. For example, Special Publication No. 51-50219, Special Publication No. 61-36532
No. 61-36534 discloses a resin plate made by copolymerizing (meth)acrylonitrile and (meth)acrylic acid with a blowing agent such as lower alcohol, formamide, monomethylformamide, etc.
A heat-resistant polyimide foam material is described that is heated and foamed at °C and simultaneously imidized. These foam materials have a density of 0
, about 03 to 0.2 g/cm', and has a heat resistance of 180°C, which can withstand the molding temperature of ordinary composite materials. However, the water absorption properties of these materials are very poor. For example, if immersed in water at 70℃, 4
It shows a significant weight increase of 60% by weight. This is significantly higher than that of polyurethane and polyvinyl chloride foam materials, which increase in weight by only several tens of percent when water is absorbed under the same conditions. For this reason, both the resin board and the foam before foaming absorb a lot of moisture, and if stored at room temperature, it is necessary to dry them before use. On the other hand, JP-A-61-272247
The publication describes a polyimide foam material with improved hygroscopicity. These materials have low hygroscopicity and can be stored at normal room temperature, and when immersed in water at 70°C,
This is a 325% weight increase per day, which is lower than conventional products, but
This is still at a high level compared to polyurethane and polyvinyl chloride foams. Furthermore, since both materials are polymerized together with foaming materials such as lower alcohols and formamide, which have low boiling points, it is not possible to raise the polymerization temperature;
Because it requires time, low temperature, and long hours, there are also problems in terms of productivity and economy.

[Means to solve the problem]

As a result of various studies on the above-mentioned problem, the present inventors found that
As a blowing agent, at least one selected from tert-butyl (meth)acrylate polymer and tert-butyl methacrylate-tert-butyl acrylate copolymer;
By using a seed polymer, it can be polymerized at high temperature and in a short time,
Moreover, the present invention was completed by discovering that it is possible to produce a heat-resistant foam material with low water absorption.

The present invention combines a structural unit represented by the following formula % formula % (1) (R in the formula represents a hydrogen atom or a methyl group) and a structural unit represented by the following formula % formula % () (in the formula R represents a hydrogen atom or a methyl group). (representing a methyl group) is 273 to 3/2 (molar ratio), and the formula (
100 parts by weight of a copolymer (A) with a molecular weight of 50,000 to 500,000 in which the total of structural units represented by Contains 1 to 100 parts by weight of a homopolymer and/or copolymer (B) with a molecular weight of 50,000 to 500,000, represented by the structural unit of (atom or methyl group), which is heat resistant and has low water absorption when heated. It is a resin composition that provides flexible foamed plastics.

Individual R in the structural units represented by formulas (1) to (I[[)
and R1 may be the same or different.

The present invention further provides a polymerizable monomer containing at least 20% by weight of a polymerizable monomer mixture in which the ratio of (meth)acrylic acid to (meth)acrylonitrile is 2/3 to 3/2 (mole ratio). At least one polymer selected from tert-butyl methacrylate polymer, tert-butyl acrylate polymer, and tert-butyl methacrylate-tert-butyl acrylate copolymer per 100 parts by weight of the polymer mixture. 1 to 100 parts by weight and a polymerization initiator are dissolved, and a copolymer obtained by heating and polymerizing at 50 to 120°C is heated and foamed. be.

The heating temperature for producing foamed plastics is 180℃.
~240°C is preferred.

The charging ratio of (meth)acrylic acid and (meth)acrylonitrile in the present invention is in the range of 2/3 to 3/2 (molar ratio). When the charged molar ratio is outside this range, each polymerizable monomer tends to form a homopolymer, making it difficult for the imidization reaction to occur. In addition, particularly when the content of (meth)acrylonitrile is high, the foam tends to darken or become brittle due to polymerization of the nitrile groups in the side chains, which is undesirable.

In the present invention, a polymerizable monomer mixture containing 20% by weight or more of this mixture of (meth)acrylic acid and (meth)acrylonitrile is used. If this content is less than 20% by weight, the imidization rate will be low and the heat resistance of the resulting foamed material will be reduced.

Polymerizable unsaturated monomers added to this mixture include lower alkyl esters such as (meth)acrylamide, N-methyl (meth)acrylamide, and (meth)acrylic acid;
Examples include cyclohexyl, but other unsaturated polymerizable monomers can also be used as long as they are copolymerizable with (meth)acrylic acid or (meth)acrylonitrile.

In the present invention, at least one polymer of tert-butyl (meth)acrylate or a copolymer thereof is used as a blowing agent. This is because when the tertiary butyl (meth)acrylate polymer is heated to a temperature of 180° C. or higher, the tertiary butyl group is eliminated as isobutyne, and this isobutyne acts as a blowing agent. The present invention has various features by using the above polymer as a blowing agent. First, the carboxyl group formed after isobutyne is eliminated reacts with the nitrile group of (meth)acrylonitrile to form a (meth)acrylimide group, resulting in a heat-resistant material. Secondly, since no blowing agent with a low boiling point is used, it becomes possible to raise the polymerization temperature and shorten the polymerization time, which is advantageous in terms of productivity and economy. In addition, the imidization reaction progresses more easily, the water absorption of the resin is reduced, the storage stability is improved, and the deterioration of properties due to water absorption is reduced.

The polymer that is the blowing agent is prepared by polymerizing tert-butyl methacrylate and tert-butyl acrylate alone or by mixing the two in an arbitrary ratio at 50 to 120°C in the presence of a radical polymerization initiator. can be easily obtained by The polymerization method may be any of bulk polymerization, emulsion polymerization, and suspension polymerization, but suspension polymerization is preferred because it yields a burl-shaped polymer that is easy to handle and dissolve.

Preferred radical polymerization initiators include benzoyl peroxide, t-butyl perpivalate, azobisisobutyronitrile, and the like.

The amount of tert-butyl (meth)acrylate polymer used as a blowing agent varies depending on the density of the desired foam.
The amount is in the range of 1 to 100% by weight, preferably 5 to 50% by weight, based on the polymerizable unsaturated monomer mixture containing (meth)acrylic acid and (meth)acrylonitrile. If the amount used is less than 1% by weight, the foamability will be insufficient, and if it is more than 100% by weight, the polymer will become brittle, which is not preferable.

In the present invention, a tert-butyl (meth)acrylate polymer as a blowing agent is dissolved in a polymerizable unsaturated monomer mixture containing 20% by weight or more of (meth)acrylic acid and (meth)acrylonitrile, and a radical A foamable copolymer is obtained by bulk polymerizing the mixture to which a polymerization initiator has been added by heating to a temperature of 50 to 120°C, preferably 60 to 100°C.

Expandable copolymers are usually created by the glass cell casting method using a spacer made of vinyl chloride, so the thickness can be adjusted arbitrarily, but conditions such as polymerization temperature must be adjusted in consideration of polymerization heat generation, etc. requires sufficient attention.

Since the composition of the present invention can be polymerized at high temperatures and in a short time, it can also be manufactured by a continuous sheet-making method using a stainless steel belt.

As the radical polymerization initiator, peroxides such as benzoyl peroxide and t-butyl pivalate, and azo compounds such as azobisisobutyronitrile are preferred.

The copolymer thus obtained is foamed by heating to 180 to 240°C, and foams 5 to 20 times by 0.05 to 0.
A density of 25 g/cm3 is obtained. The resulting foam also has heat resistance up to about 180°C.

The foamed material according to the present invention can be used alone as a heat-resistant heat insulating material or a sound absorbing material, and can also be used as a structure made by hardening a plate-shaped foamed material sandwiched between both sides of a reinforced fiber reinforced material called prepreg impregnated with a thermosetting resin. It can be advantageously used as As the reinforcing fiber, any organic fiber such as carbon fiber, glass fiber, or Kevlar (registered trademark) can be used.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples. In the examples, polymerizable monomers are indicated by the following abbreviations.

Methacrylic @: MAA Acrylic acid: AA Methacrylonitrile: MAN Acrylonitrile: AN Tertiary butyl methacrylate: TBMA Tertiary butyl acrylate: TBA Reference Example I Production of TBMA homopolymer: The TBMA polymer used as a blowing agent was prepared as follows. Manufactured according to the procedure. 100 parts of ion-exchanged water, 0.2 parts of sodium acrylate and 0.2 parts of sodium sulfate as dispersion stabilizers.
15 parts were placed in a separable flask purged with nitrogen and stirred to dissolve the dispersion stabilizer and sodium sulfate. Separately, 0.00 parts of TBMAI and 0.00 parts of azobisisobutyronitrile.
One part of the solution was dissolved and put into the above-mentioned separable flask. After adding the water, stir vigorously and start heating with the water dispersed in the water. Heating was continued while checking the bath temperature. An exothermic peak of polymerization occurred 90 minutes after the internal temperature became constant (77°C). Heating was continued for about 30 minutes after the peak (83°C) appeared, and heating was stopped after polymerization was completed. After washing the obtained bead-shaped polymer with ion-exchanged water, TBM was prepared by heating and drying at 60°C.
Polymer A was obtained.

Example 1 50 parts by weight of MAA and 50 parts by weight of MAN were uniformly mixed, 16 parts by weight of the TBMA polymer obtained in Reference Example 1 was added, and the mixture was stirred and dissolved at room temperature.

After uniform dissolution, 2 parts by weight of azopisisobutyronidine was dissolved. This homogeneous melt was poured into a cell with a polyvinyl chloride spacer sandwiched between two glass plates.
When the resin was cured by heating at 80° C. for 2 hours, an opaque resin plate was obtained.

By heating this resin at 200°C for 2 hours, a polymethacrylimide foam having a density of 0°06 g/cm' was obtained. Further, by heating the same resin plate at 220°C for 2 hours, a foamed material having a density of 0.04 g/cm' was obtained.

The obtained foamed material was cut into pieces of length 100 mm x width 100 mm x thickness 25 mm, dried at 70°C for 48 hours, and then
When a moisture absorption test was conducted at 0t x 95% RH, the moisture absorption amount was saturated in 2 days and a weight increase of 3.5% was observed. There was almost no difference in water absorption depending on foam density.

Example 2 and Comparative Example 1 Example 1 except that the amount of TBMA polymer as a blowing agent was changed.
A resin plate was obtained in the same manner. This resin plate was heated to 200℃ for 2 hours.
By heating for a period of time, foamed materials having various densities shown in Table 1 were obtained. The amount of TBMA polymer added in the table is MA
It means the amount added to a mixture of 50 parts by weight of A and 50 parts by weight of MAN.

Table 1 Experiments NCL 1 and 6 are examples using compositions in which the amount of TBMA polymer added is outside the range of the present invention. Compared to the materials obtained in these experiments, experiment N112, which is within the scope of the present invention,
It can be seen that the ~50 foam is a material that foams uniformly and has a low amount of moisture absorption.

Example 3 The foamed material obtained in Example 1 was mixed into 100III1×11
It was cut into 0011111×25 pieces and dried at 70° C. for 48 hours. After accurately measuring the length, radius and thickness of this foam, it was heated at 180° C. for 2 hours and the dimensions of the foam were measured. The dimensional deformation of the foam before and after heating was less than 1 dimensional, indicating that it could withstand the curing temperature of ordinary CFRP sandwich boards.

Example 4 30 parts by weight of MAA, 40 parts by weight of MAN and 30 parts by weight of cyclohexyl methacrylate were added as polymerizable monomers and stirred to obtain a homogeneous polymerizable monomer mixture.

A milky white resin board was obtained by making a board from this mixture in the same manner as in Example 1. By heating the obtained resin plate at 200°C for 2 hours, the density becomes 0.05 g/cn+
A uniform foam of No. 3 was obtained. This foam was dried and moisture-absorbed in the same manner as in Example 1. The water absorption amount was 2.6% by weight, and a foam with low water absorption was obtained.

Applicant: Mitsubishi Rayon Co., Ltd. 〃 Mitsubishi Heavy Industries, Ltd Agent: Patent Attorney Atsushi Takahashi -

Claims (1)

[Claims] A structural unit represented by the following formula ▲ Numerical formula, chemical formula, table, etc. ▼ (I) (R in the formula represents a hydrogen atom or a methyl group) and the following formula ▲ Numerical formula, chemical formula, There are tables, etc. ▼ (II) (R in the formula represents a hydrogen atom or a methyl group) The ratio of the structural units represented by the formula is 2/3 to 3/2 (molar ratio), and the formula (
I) and a molecular weight of 50,000 to 500,000 in which the sum of the structural units represented by formula (II) is at least 20% by weight
100 parts by weight of polymer (A) and the following formula ▲ Numerical formula, chemical formula, table, etc. ▼ (III) (R^1 in the formula represents a hydrogen atom or a methyl group) Molecular weight 50,000 expressed by the structural unit A resin composition containing 1 to 100 parts by weight of a homopolymer and/or a copolymer (B) of 500,000 to 500,000, which gives a heat-resistant and low water absorption foamed plastic when heated. (2) The ratio of methacrylic acid and/or acrylic acid to methacrylonitrile and/or acrylonitrile is 2/
Tert-butyl methacrylate polymer, tert-butyl acrylate to 100 parts by weight of a polymerizable monomer mixture containing at least 20% by weight of a polymerizable monomer mixture composed of 3 to 3/2 (molar ratio). At least one polymer selected from polymers, tert-butyl methacrylate-tert-butyl acrylate copolymers 1 to 100
1. Production of heat-resistant and low water-absorbing foamed plastics, which is characterized by heating a copolymer obtained by dissolving parts by weight and a polymerization initiator and polymerizing by heating at 50 to 120°C. (3) The method according to claim 2, wherein the heating temperature is 180 to 240°C.