JPH04170408A - Expandable plastics and foamed plastic manufacturing methods - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention can be converted into poly(meth)acrylimide foam (methacrylimide foam or acrylimide foam, hereinafter the same description) by heating. Regarding foamable plastics.

[Problems to be solved by the prior art and the invention]

Foamed materials used as heat insulating or soundproofing materials include polyurethane foam, polyvinyl chloride foam, and many other materials. In recent years, these foamed materials have been used as structural materials for airplanes and the like, and as core materials for composite sanderch boards. This is due to the difficulty in adhering or repairing conventionally used honeycomb structures. However, there is no conventional foam material that can withstand the molding temperature or pressure of a sandwich structure.

Various studies have been conducted to address the problems of heat resistance and pressure resistance. For example, Japanese Patent Publication No. 52-5[)219, Japanese Patent Publication No. 61-36532, and Japanese Patent Publication No. 61-3653.
Publication No. 4 describes a heat-resistant resin plate in which (meth)acrylonitrile and (meth)acrylic acid are copolymerized together with a blowing agent such as a lower alcohol, formamide, monomethylformamide, etc., which is heated and foamed at 180 to 220°C and simultaneously imidized. Polyimide foam materials are described.

These foam materials have a density of 0.03-0.2g/cm3
It is relatively lightweight and has a heat resistance of 180°C, which means it can withstand the molding temperature of ordinary composite materials. However, these materials have very poor water absorption. For example, when immersed in water at 70°C, it shows a significant weight increase of 460% in 50 days. This is significantly higher, about 10 times higher than that of polyurethane/polyvinyl chloride foam, which increases in weight by only several tens of percent when water is absorbed under the same conditions. Therefore, both the resin and the foam before foaming have a high moisture absorption, and when stored at room temperature, it is necessary to dry them before use.

On the other hand, JP-A-61-272247 describes a polyimide foam material with improved hygroscopicity. These materials have low hygroscopicity and can be stored at normal room temperature conditions. However, when immersed in water at 70°C, the increase was 325% by weight in 50 days, which is lower than the conventional product but still at a high level. In addition, since all materials are polymerized together with blowing agents such as lower alcohols and formamide,
It is also problematic in terms of productivity and economy that the polymerization temperature cannot be raised and that it takes a long time at a low temperature of 40 to 60°C for 20 to 40 hours.

[Means to solve the problem]

As a result of various studies in view of the above problems, the present inventors found that by combining tert-butyl (meth)acrylate and (meth)acrylonitrile, it is possible to polymerize at high temperature and in a short time, and also by using a special blowing agent. The present invention has been completed based on the discovery that it is possible to produce a foamed material with low moisture absorption and heat resistance without using any of the above methods.

The present invention provides a structural unit represented by the formula % (in which R is a hydrogen atom or a methyl group), and a structural unit represented by the formula % (in which R is a hydrogen atom or a methyl group), which provides a new foamed plastic that is heat resistant and has low water absorption when heated. % formula % () (R in the formula is a hydrogen atom or a methyl group) The ratio of structural units is 273 to 3/2 (molar ratio), and the structure is represented by formulas (1) and (I[) Molecular weight from 50,000 to 500, the total of the units being at least 20% by weight in the copolymer
000 copolymer.

The present invention further provides that the ratio of tert-butyl methacrylate and/or tert-butyl acrylate to methacrylonitrile and/or acrylonitrile is 2/3 to 3/3.
2. Polymerizing a polymerizable monomer mixture containing at least 20% by weight of a polymerizable monomer consisting of (molar ratio),
This is a method for producing new foamed plastics that is heat resistant and has low water absorption, which is characterized by heating the resulting copolymer.

The foamed plastics of the present invention contain 18% of the above copolymer.
By heating to 0 to 240°C, it can be produced without the need for a special blowing agent.

The charging ratio of tert-butyl (meth)acrylate and (meth)acrylonitrile used in the present invention is tert-butyl (meth)acrylate/(meth)acrylonitrile=2
It is in the range of 73 to 3/2 (molar ratio). If the molar ratio of the charged material is outside the above range, there is a high possibility that each polymerizable monomer will become a homopolymer. In particular, if the content of (meth)acrylonitrile is high, the polymerization of the nitrile group in the side chain will cause the foam to form. It becomes dark or brittle, which is not desirable.

In the present invention, a polymerizable monomer mixture containing 20% by weight or more of a tertiary butyl (meth)acrylate/(meth)acrylonitrile mixture is used. This content is 20% by weight
If it is lower than this, the foaming performance will deteriorate and the imidization rate will decrease, resulting in a decrease in the heat resistance of the resulting foam.

Other polymerizable unsaturated monomers to be added to the tert-butyl (meth)acrylate/(meth)acrylonitrile mixture include (meth)acrylamide, N-methyl (meth)
(meth)acrylamide compounds such as acrylamide, (
Lower alkyl esters of meth)acrylic acid, cyclohexyl (meth)acrylate, etc. are preferred, but other copolymerizable unsaturated monomers such as styrene, fluorine-containing polymerizable unsaturated monomers, etc. can also be used.

In the present invention, there is no need to use a special blowing agent because when tertiary-butyl (meth)acrylate is heated to 180°C or higher, the tertiary-butyl group is eliminated as isobutyne, and this isobutyne acts as a blowing agent. It's for a reason.

Further, the carboxyl group after isobutyne is eliminated and the nitrile group of (meth)acrylonitrile, which is the other component, react to form a (meth)acrylimide structure, resulting in a heat-resistant material.

The foamable copolymer of the present invention has a ratio of (meth)acrylic tert-butyl to (meth)acrylonitrile of 2/2.
It can be produced by polymerizing a polymerizable monomer mixture containing at least 20% by weight of a polymerizable monomer composed of 3 to 3/2 (molar ratio) by a known method.

As a polymerization method, in the presence of a radical polymerization initiator, 50
It is preferable to use a method of bulk polymerization at a temperature of ~120°C, preferably 60~100°C.

During the polymerization reaction, it is necessary to pay sufficient attention to the polymerization temperature and other conditions in consideration of polymerization heat generation and the like.

Preferred examples of the radical polymerization initiator include benzoyl peroxide, t-butyl perpivalate, and azobisisobutyronitrile.

The copolymer is foamed by heating to 180 to 240°C, and has a density of 0.02 to 0.25 g/cc when expanded 5 to 40 times.
A foam is obtained. This foam has a heat resistance up to about 180°C.

The present invention has a number of other great features in addition to the great effect that a heat-resistant foamed material can be obtained without using a blowing agent.

First, since a low-temperature foaming foaming agent is not used, the polymerization temperature can be raised and the polymerization time can be shortened, which is advantageous in terms of productivity and economy.

Furthermore, tert-butyl (meth)acrylate and (meth)
The copolymerizability with acrylonitrile is better than that of the conventional combination of (meth)acrylic acid and (meth)acrylonitrile. That is, tertiary butyl (meth)acrylate and (meth)acrylonitrile are likely to undergo random copolymerization, and the subsequent imidization proceeds favorably. On the other hand, (meth)acrylic acid and (meth)acrylonitrile tend to form a block polymer in which (meth)acrylic acid polymerizes first, and the imidization reaction does not occur. The body tends to become dark and brittle. Furthermore, by using tertiary butyl (meth)acrylate, the hygroscopicity of the resin before foaming is reduced, storage stability is improved, and furthermore, it is expected that the material after foaming will have lower water absorption. This is thought to be because conventional materials had carboxyl groups with high hydrophilicity, whereas the resin of the present invention has tertiary butyl groups with lower hydrophilicity.

The foamed material according to the present invention can be used alone as a heat insulating material for heat-resistant applications.
In addition to being used as a sound absorbing material, it can also be advantageously used as a structure made by hardening a material sandwiched between a reinforced fiber reinforcing material (so-called prepreg) in which both sides of a plate-shaped foam material are impregnated with a thermosetting resin. As the reinforcing fibers, carbon fibers, glass fibers, organic fibers such as Kevlar, etc. can be used.

〔Example〕

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

Tertiary butyl methacrylate: TBMA Tertiary butyl acrylate: TBA methacrylonitrile
: MAN acrylonitrile : AN methacrylic acid : MAA Example 1゜TBMA 70 parts by weight, MAN 30 parts by weight (molar ratio TBM
A/MA'N=1.11> and 2 parts by weight of azoisobutyronitrile were uniformly mixed. Continue adding this mixture to 2
It was poured between cells with a polyvinyl chloride spacer sandwiched between sheets of glass, and cured at 80° C. for 2 hours. A transparent and uniform resin plate was obtained.

By heating this resin plate at 200°C for 2 hours, the
．． A polymethacrylimide foam with a density of 0.05 g/cm' was obtained.

In addition, by heating at 220°C for 2 hours, 0.03
A foamed material with a density of g/cm3 was obtained.

The length of the obtained foam material is 100o + rnx radius 100m
After cutting to a thickness of 25 mm and drying at 70° C. for 48 hours, a moisture absorption test was conducted at 95% RH. On the second day, the moisture absorption amount reached saturation and showed an increase of 4.1% by weight. There was almost no difference in moisture absorption depending on foam density.

Comparative Example 1 60 parts by weight of MAA, 40 parts by weight of M A N (molar ratio M
AA/MAN=1.17) A homogeneous mixture consisting of 1 part by weight of formamide, 1 part by weight of isopropyl alcohol and 0.2 part by weight of t-butyl perpivalate was heated at 40°C for 70 hours in the same manner as in Example 1. A transparent resin plate was obtained by further heating at 110° C. for 20 hours. By heating this resin at 200°C for 2 hours, a polyimide foam material having a density of 0.05 kg/cm' was obtained.

When the obtained foamed material was subjected to moisture absorption under the same conditions as in Example 1, the saturated moisture absorption amount increased by 8% by weight, which was a large value.

From the above results, the resin composition of the present invention is cured at high temperature in a short time, and a foam can be obtained without particularly adding a foaming agent. It can also be seen that the amount of moisture absorbed by the foamed material obtained is lower than that of conventional products.

Example 2, Comparative Example 2 The composition shown in Table 1 was used as the polymerizable monomer mixture, and heated at 80° C. for 2 hours in the same manner as in Example 1 to obtain a transparent resin plate. The obtained resin plate was heated at 200° C. for 2 hours to obtain a foam. The density of the obtained foam and 70
Table 1 also shows the saturated water absorption amount under the conditions of ℃ and 95% RH.
Shown below.

Example 3 The foamed material obtained in Example 1 was 100 mm x 100 m.
It was cut into rnX 25 mm pieces and dried at 70°C for 48 hours.

After measuring the length, width, and thickness of this foam, it was heated at 180° C. for 2 hours and the dimensions of the foam were measured again. It can be seen that the dimensional deformation of the foams after heating was 1 mrn or less in all cases, and that they sufficiently withstood the curing conditions of ordinary CFRP sandwiches.

Claims (3)

[Claims] (1) Formulas that produce foamed plastics with heat resistance and low water absorption when heated ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (I) Structure represented by (R in the formula is a hydrogen atom or a methyl group) The ratio of the structural unit represented by the unit and formula ▲ Numerical formula, chemical formula, table, etc. ▼ (II) (R in the formula is a hydrogen atom or methyl group) is 2/3 to 3/2 (molar ratio), and expression (I)
The total number of structural units represented by (II) and (II) in the total copolymer is
molecular weight of at least 20% by weight from 50,000 to 500
000 copolymer. (2) Tert-butyl methacrylate and/or tert-butyl acrylate and methacrylonitrile and/or
or a polymerizable monomer mixture having a ratio of 2/3 to 3/2 (molar ratio) to acrylonitrile of at least 20%.
1. A method for producing a new heat-resistant and low water absorption foamed plastic, which comprises polymerizing a polymerizable monomer mixture containing % by weight and heating and foaming the resulting copolymer. (3) The method according to claim 2, wherein the heating temperature is 180 to 240°C.