WO2019052360A1

WO2019052360A1 - Process for injection moulding polymer compounds comprising poly (meth) acrylimide foam particles

Info

Publication number: WO2019052360A1
Application number: PCT/CN2018/103794
Authority: WO
Inventors: Ricardo Luiz Willemann; Qianwen KONG; Pei HU; Huifeng LU
Original assignee: Evonik Specialty Chemicals Shanghai Co Ltd
Current assignee: Evonik Specialty Chemicals Shanghai Co Ltd
Priority date: 2017-09-18
Filing date: 2018-09-03
Publication date: 2019-03-21
Anticipated expiration: 2020-03-18

Abstract

Provided is a process for injection moulding a polymer compound comprising a thermoplastic resin which is melt processible at temperatures of less than 400°C, and poly (meth) acrylimide (P (M) I) foam particles which maintain the particulate form at a temperature at least 100°C higher than the Tg of the thermoplastic resin. The process includes steps of: (a) heating the polymer compound to a temperature 100-200°C higher than the Tg of the thermoplastic resin, and (b) injecting the polymer compound to a mould under an injection pressure of 100-3000 bar. The injection moulding obtained from the method achieves better mechanical performance than the individual components, and can be widely used in lightweight design.

Description

PROCESS FOR INJECTION MOULDING POLYMER COMPOUNDS COMPRISING POLY (METH) ACRYLIMIDE FOAM PARTICLES

Field of the invention

The invention relates to a process for injection moulding polymer compounds comprising poly (meth) acrylimide (P (M) I) foam particles, in particular polymethacrylimide (PMI) foam particles.

Background

Poly (meth) acrylimide foams e.g. polymethacrylimide foams, such as those marketed under the trademark

by Evonik Resource Efficiency GMBH, are widely used in composite material for light weight design in the aerospace, automotive, sport and medical device industries, etc. due to their light weight and high mechanical performance.

In the past, the P (M) I foams were supplied in the shape of blocks, which however did not quite fit the processing of parts with complex 3D geometries, and could result in long cycle time, low precision, and material waste.

WO2013/056947 describes a mould shaping process of P (M) I foams which partially solves the above problems, wherein (prefoamed) P (M) I polymer particles are foamed in a mould with the aid of adhesives, which can be a polyamide or a poly (meth) acrylate. The dose of the adhesives can be up to 20%of the P (M) I polymer particles, i.e. up to 16.7%based on the total weight of the P (M) I polymer particles and the adhesive. However this process still results in long cycle time.

PCT/CN2017/078572 describes a polymer compound comprising poly (meth) acrylimide (P (M) I) foam particles. The present inventors further explored the process for injection moulding the described polymer compound and accomplished the present invention.

Summary of the present invention

The present invention provides a process for injection moulding a polymer compound comprising:

(1) 20-99%a thermoplastic resin, which is melt processible at temperatures of less than 400℃, and

(2) 1-80%poly (meth) acrylimide (P (M) I) foam particles, which maintain the particulate form at a temperature at least 100℃ higher than the T _g of the thermoplastic resin,

based on the total weight of the polymer compound,

said process including steps of:

(a) heating the polymer compound to a temperature 100-200℃ higher than the T _g of the thermoplastic resin where the thermoplastic resin melts and the poly (meth) acrylimide (P (M) I) foam particles maintain the particulate form, and

(b) injecting the polymer compound to a mould under an injection pressure of 100-3000 bar.

T _g refers to glass transition temperature, which can be determined by the DSC method according ISO 1135.

The present inventor has found it is important to control the temperature and pressure during the injection moulding process so as to provide sufficient flowability of the polymer compound, and to avoid the damage of the cell structure of the foam particles.

And it is surprisingly found that the injection mouldings obtained from the process of the present invention achieves better compressive and/or bend strength than the individual components, besides the light weight.

The present invention also provides the injection mouldings obtained from the process of the present invention.

The present invention further provides the use of the injection mouldings of the present invention in light weight design.

Detailed description of the present invention

Preferably, in step a) the temperature is 110-180℃, more preferably 120-160℃ higher than the T _g of the thermoplastic resin.

Preferably, in step b) the injection pressure is 200-2000 bar, more preferably 200-1500 bar.

Preferably, the process is carried out in an injection moulding machine having a screw, an injection nozzle and a mould, and the back pressure of the screw is 0-50 bar, more preferably 10-30 bar.

Preferably, in step b) the holding pressure is 0-30%, more preferably 0-10%of the injection pressure.

There is no limitation to the thermoplastic resin as long as it is melt processible at temperatures of less than 400℃. Melt processible is used in its conventional sense, that the polymer can be processed at the indicated temperatures without substantial degradation of the polymer.

Examples of the thermoplastic resin include polyamides, polyolefins, polyesters and copolymers containing any of the above segments as well as the blend thereof.

Preferably, the polyamide is selected from aliphatic polyamides, more preferably PA6, PA11, PA12, PA46, PA66, PA10, PA610, PA612, PA1010, PA1012 and the blend thereof.

The P (M) I foam particles used in the present invention can be obtained by the granulation of the P (M) I foams which are not in particulate form.

The P (M) I foams are also termed rigid foams, and feature particular robustness. The P (M) I foams are normally produced in a two-stage process: a) production of a cast polymer, and b) foaming of said cast polymer. In accordance with the prior art, these are then cut or sawn to give the desired shape.

Production of the P (M) I foams begins with production of monomer mixtures which comprise (meth) acrylic acid and (meth) acrylonitrile, preferably in a molar ratio of from 2: 3 to 3: 2 as main constituents. Other comonomers can also be used, examples being esters of acrylic or methacrylic acid, styrene, maleic acid and itaconic acid and anhydrides thereof, and vinylpyrrolidone. However, the proportion of the comonomers here should not be more than 30%by weight. Small quantities of crosslinking monomers can also be used, an example being allyl acrylate. However, the quantities should preferably be at most from 0.05%by weight to 2.0%by weight.

The copolymerization mixture moreover comprises blowing agents which at temperatures of about 150 to 250℃ either decompose or vaporize and thus form a gas phase. The polymerization takes place below this temperature, and the cast polymer therefore comprises a latent blowing agent. The polymerization advantageously takes place in a block mould between two glass plates.

The cast polymer is then foamed at an appropriate temperature in a second step. The production of such P (M) I foams is known in principle to a person skilled in the art and can be reviewed in EP 1 444 293, EP 1 678 244 or WO 2011/138060 for example.

The P (M) I foam particles used in the present invention can also be obtained by the foaming of the P (M) I polymer particles.

The P (M) I polymer particles can be obtained by grinding the cast polymer, for example, in a cutting mill. The grindings are then foamed at an appropriate temperature to produce the P (M) I foam particles.

Preferably, the P (M) I foam particles used in the present invention is obtained by the foaming of the P (M) I polymer particles, where the closed foam cells are not destroyed, compared with the P (M) I foam particles obtained by the granulation of the P (M) I foams.

Preferably, the P (M) I foam particles have a grain size which ranges 0.1-30 mm, more preferably 0.5-10 mm.

Preferably, the P (M) I foam particles have a bulk density of 25-220 kg/m ³, more preferably 50-150 kg/m ³.

In one embodiment of the present invention, the P (M) I foam particles are polymethacrylimide (PMI) foam particles.

PMI polymers and/or foams, commercially available from Evonik Resource Efficiency GMBH, may be mentioned in particular.

Preferably, the thermoplastic resin constitutes majority of the polymer compound to provide sufficient flowability of the polymer compound for the process of the present invention.

In such a context, the thermoplastic resin can constitute 50-99%, preferably 60-95%, more preferably 70-90%, and the P (M) I foam particles can constitute 1-50%, preferably 5-40%, more preferably 10-30%, based on the total weight of the polymer compound.

Preferably, the thermoplastic resin is melt processible at temperatures of less than 250℃, and/or the P (M) I foam particles maintain the particulate form at a temperature at least 120℃, preferably at least 160℃ higher than the T _g of the thermoplastic resin.

The polymer compound of the present invention may include additives, such as calcium carbonate, glass beads, zinc oxide, and fiber reinforcements such as ceramic fibers, aramid fibers, potassium titanate fibers, glass fibers and carbon fibers, depending on the effect or performance desired.

The injection mouldings obtained from the process of the present invention are generally suitable in principle for any type of lightweight design, and can in particular be used in mass production by way of example for structural parts in the automobile industry, in rail vehicle construction or shipbuilding, in the aerospace industry, in mechanical engineering, in the production of sports equipment, in furniture construction or in the design of wind turbines.

Examples

The PMI foam particles used in the examples were prepared from PMI polymer particles marketed with trademark

Triple F by Evonik Resource Efficiency GMBH. The PMI polymer particles were produced from a fully polymerized copolymer sheet (which had not been prefoamed) with the aid of a granulator. The grain size range of the particles used in the examples, after sieving to keep the fines, was below 1.0 mm. The bulk density of the PMI polymer particles was about 600-700 kg/m ³.

The PMI polymer particles were foamed in an oven at a temperature of 200-240℃ for 30-60 mins. The obtained PMI foam particles had a bulk density of 100-150 kg/m ³ and a grain size of 0.5-5 mm.

The PMI foam particles were mixed with the melts of a medium-viscosity copolyamide with laurolactam as the main component (T _g = 40℃, commercially available from Evonik Resource Efficiency GMBH under the tradename

N1901) to prepare a 20 : 80 (part by weight) compound, which were shaped into plates having a thickness of 5 mm by injection moulding in an injection machine (Engel Victory 200/110 Tech Pro) according to process parameters indicated in the table below. The plates were tested for compressive strength (ISO 844) and bending strength (ISO 178) as well as density. The result is indicated in the table below.

**

200 WF PMI rigid foam, commercially available from Evonik Resource Efficiency GMBH, was also selected as reference material, because of its relatively high compression and bending strength, among the marketed

series of PMI foams.

It can be seen that the injection mouldings of Examples 1-4 achieve higher compressive and/or bending strength than the individual raw materials, in addition to the low density compared with the thermal plastic resin used.

Claims

A process for injection moulding a polymer compound comprising:

(1) 20-99%a thermoplastic resin, which is melt processible at temperatures of less than 400℃, and

(2) 1-80%poly (meth) acrylimide (P (M) I) foam particles, which maintain the particulate form at a temperature at least 100℃ higher than the T _g of the thermoplastic resin,

based on the total weight of the polymer compound,

said process including steps of:

(a) heating the polymer compound to a temperature 100-200℃ higher than the T _g of the thermoplastic resin where the thermoplastic resin melts and the poly (meth) acrylimide (P (M) I) foam particles maintain the particulate form, and

(b) injecting the polymer compound to a mould under an injection pressure of 100-3000 bar.
The process according to claim 1, wherein in step a) the temperature is 110-180℃, preferably 120-160℃ higher than the T _g of the thermoplastic resin.
The process according to any one of the preceding claims, wherein in step b) the injection pressure is 200-2000 bar, preferably 200-1500 bar.
The process according to any one of the preceding claims, wherein the process is carried out in an injection moulding machine having a screw, an injection nozzle and a mould, and the back pressure of the screw is 0-50 bar, preferably 10-30 bar.
The process according to any one of the preceding claims, wherein in step b) the holding pressure is 0-30%, preferably 0-10%of the injection pressure.
The process according to any one of the preceding claims, wherein the thermoplastic resin is selected from polyamides, polyolefins, polyesters and copolymers containing any of the above segments as well as the blend thereof, preferably from aliphatic polyamides, more preferably from the group consisting of PA6, PA11, PA12, PA46, PA66, PA10, PA610, PA612, PA1010, PA1012 and the blend thereof.
The process according to any one of the preceding claims, wherein the P (M) I foam particles have a grain size which ranges 0.1-30 mm, preferably 0.5-10 mm, and /or a bulk density of 25-220 kg/m ³, preferably 50-150 kg/m ³.
The process according to any one of the preceding claims, wherein the P (M) I foam particles are obtained by the granulation of P (M) I foams which are not in particulate form, or the foaming of P (M) I polymer particles.
The process according to any one of the preceding claims, wherein the P (M) I foam particles are polymethacrylimide (PMI) foam particles.
The process according to any one of the preceding claims, wherein the polymer compound comprises:

50-99%, preferably 60-95%, more preferably 70-90%the thermoplastic resin, and

1-50%, preferably 5-40%, more preferably 10-30%the P (M) I foam particles,

based on the total weight of the polymer compound.
The process according to any one of the preceding claims, wherein

the thermoplastic resin is melt processible at temperatures of less than 250℃,

and/or

the P (M) I foam particles maintain the particulate form at a temperature at least 120℃, preferably at least 160℃ higher than the T _g of the thermoplastic resin.
The process according to any one of the preceding claims, wherein the polymer compound is in situ made in step a) by physically mixing the P (M) I foam particles and the melt of the thermoplastic resin.
Injection mouldings obtained from the process according to any one of the preceding claims.
Use of the injection mouldings according to claim 13 in light weight design.