[Solved]-highchart save image using exporting java and phantomjs-Highcharts

Open AbstractPool.java file, in line 117 you can find:

    Collection<File> oldFiles = FileUtils.listFiles(TempDir.outputDir.toFile(),filter, null);
    for (File file : oldFiles) {
        file.delete();
    }

Simply delete that lines, and should be enough. Or above that lines you can set higher fixedRate.

In addition to Pawel's answer you can also change the time limit in the app-convert.properties file:

# Keep files in the temp folder for a certain retentionTime, defined in miliseconds
retentionTime = 30000 

That is the default. So, 30s makes sense.