highchars之IE8浏览器下 X轴文字显示重叠应如何解决

页面为教师端首页查看教师端下各个班级所有学生考试成绩统计曲线图，谷歌浏览器显示如下：

IE8浏览器下，X轴文字重叠，页面显示如下：

 

JS：

function LoadClassAssess(classId) {
        if (classId > 0) {
            $.ajax({
                type: "post",
                url: "/Teacher/HomeManage/GetClassAssessGra/",
                cache: false,
                data: { classId: classId, pageIndex: _pageIndex, newtime: new Date().getTime() },
                success: function (data) {
                    _pageIndex = data.pageIndex;
                    _totalPage = data.totalPage;
                    _currentPage = data.AName.length;
                    //左边按钮样式
                    if (_pageIndex>0) {
                        $(".prev2").removeClass("arrowN").addClass("arrowB");
                    }
                    else {
                        $(".prev2").removeClass("arrowB").addClass("arrowN");
                    }
                    //右边按钮样式
                    if (_totalPage>_pageIndex+_currentPage) {
                        $(".next2").removeClass("arrowN").addClass("arrowB"); 
                    }
                    else {
                        $(".next2").removeClass("arrowB").addClass("arrowN");
                    }
                    //图形加载
                    var chart = new Highcharts.Chart({
                        chart: {
                            renderTo: 'containerAssess',
                            type: 'line',
                            width: 1100,
                            height: 219,
                            marginTop: 35
                        },
                        colors: ['#FF6EC7', '#32CD99', '#24CBE5'],
                        plotOptions: {
                            spline: {
                                lineWidth: 1.5,
                                marker: {
                                    enabled: false,
                                    states: {
                                        hover: {
                                            enabled: true,
                                            symbol: 'square',
                                            radius: 2
                                        }
                                    }
                                }
                            }
                        },
                        title: {
                            text: '',
                            x: -20 //center
                        },
                        subtitle: {
                            text: '',
                            x: -20
                        },
                        xAxis: {
                            labels: {
                                style: {
                                    'fontSize': '10px'
                                }
                            },
                            categories: data.AName//原格式输出@Html.Raw();
                        },
                        yAxis: {
                            title: {
                                text: ''
                            },
                            tickInterval: 50,
                            max: 100,
                            min: 0,
                            plotLines: [{
                                value: 0,
                                width: 1,
                                color: '#808080'
                            }]
                        },
                        tooltip: {
                            valueSuffix: '',
                            shared: true,
                            useHTML: true
                        },
                        series: [{
                            name: '平均分',
                            data: data.Average
                        }, {
                            name: '最高分',
                            data: data.MaxGrade
                        }, {
                            name: '最低分',
                            data: data.MinGrade
                        }]
                    });
                }
            });
        }
    };

　请大神给予技术指导，在此谢过！！！